I would suggest that you look again at this hazard.
The Aw required for growth of Clostridium botulinum is approx. 0.95 although the literature may vary.
Products such as cakes are going to have an Aw much lower than this so you won't get the growth.
The following link is quite good.
http://www.labcell.c...bcell-email.pdf
If you are concerned I'd get the Aw checked on your product but I believe that your average cake with its relatively high sugar content will have a lower Aw than is required for the growth of C.botulinum. Cakes fall within the Aw range that are more likely to be affected by yeasts and moulds than bacteria.
Hi Hobgloblin,
Thks yr input/table. Useful stuff.
Terminologies are always a potential minefield in threads like this one, eg "average" cake. 
I have seen an Aw as low as 0.93 (USFDA) mentioned for C.botulinum growth. As you say, it depends.
I enclose a list of "high moisture" bakery items which accompanied the C.botulinum comment within my attachment/post 2
high moisture bakery items.pdf 9.74KB
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The above list includes various "cakes" of "high" Aw but whether the OP/others would regard any of them as potentially "ambient" I have no idea. (Relates to numerical "shelf-life" of course). Just as illustration -
http://stilltasty.co...ems/index/16654
I presume the USFDA would consider all the listed items above as TCS (ie non-shelf stable) based on a 0.85 Aw limit but the terminology "shelf stable" seems itself to have some flexibility in the USA cake arena, eg -
We analyzed the filling and then we analyzed the filling/cookie or cake interface (where the cookie or cake touches the filling).
All of the frostings and fillings are below 0.850 which means these cookies and cakes can be considered shelf-stable, but for only 3 days (!!) for the following products: the vanilla cream cheese, classic buttercream and the clothespin cookies. These products had an interface reading above 0.850. So after 3 days, they should be refrigerated so they have a limited shelf-life.
The only product that would truly (!!) be considered to be shelf-stable was your All Butter Cream frosting and cake which had both readings below 0.850.
http://www.cakecentr...elf-stable-what
Nonetheless, according to this article, there were no reported events of baked products/C.botulinum reported up to 2002 -
MAP technology in baking Industry,2002.pdf 402.83KB
31 downloads
PS - this publication seems to be a primary, albeit somewhat ageing, reference but unfortunately requires $ -
https://www.ncbi.nlm...pubmed/15077880
Shelf life and Safety concerns of bakery products--a review. Smith et al (2004)
Abstract
Bakery products are an important part of a balanced diet and, today, a wide variety of such products can be found on supermarket shelves. This includes unsweetened goods (bread, rolls, buns, crumpets, muffins and bagels), sweet goods (pancakes, doughnuts, waffles and cookies) and filled goods (fruit and meat pies, sausage rolls, pastries, sandwiches, cream cakes, pizza and quiche). However, bakery products, like many processed foods, are subject to physical, chemical and microbiological spoilage. While physical and chemical spoilage limits the shelf life of low and intermediate moisture bakery products, microbiological spoilage by bacteria, yeast and molds is the concern in high moisture products i.e., products with a water activity (a(w)) > 0.85. Furthermore, several bakery products also have been implicated in foodborne illnesses involving Salmonella spp., Listeria monoctyogenes and Bacillus cereus, while Clostridium botulinum is a concern in high moisture bakery products packaged under modified atmospheres. This extensive review is divided into two parts. Part I focuses on the spoilage concerns of low, intermediate and high moisture bakery products while Part II focuses on the safety concerns of high moisture bakery products only. In both parts, traditional and novel methods of food preservation that can be used by the bakery industry to extend the shelf life and enhance the safety of products are discussed in detail.
