Unfortunately, insulin injections are often cheaper than the pump. If this person doesn't have decent medical insurance, the injections are likely the most affordable for him. Downside is that there is a steep learning curve for figuring out how to time your injections so you don't crash and need the "snack" (probably a glucose tab).
Keep in mind you may also have to adjust your sharps/foreign material program to accommodate this. If he's allowed in any production areas from receiving raw materials to shipping finished goods, you need to ensure that there is 0 chance of those used injections being present in your product. That means having a specific sharps disposal device he needs to use, with firm disciplinary action if he disposes of them in the regular trash.
Do you have water stations set up near production areas? Ex: a water cooler with disposable cups. That may be a solution for where he can store his cooler. Or perhaps if you have a first aid kit located nearby the production area it could be kept near there? Or maybe on a production supervisor or manager's desk? Also, depending on how hot your facility gets, a cooler might not keep the insulin cold enough during a shift.
You'll want to work with HR and/or legal on this as well to ensure your solutions don't cross any legal (HIPPA) lines and that you've tried to offer reasonable accommodation under ADA law. Depending on the nature of your operation, reasonable accommodation for this person may not be possible, and that's where you want HR and legal to be on the same page with you.