I’d go with Paul’s method. If you can get all the way through, use copper wire which you can bend over so it won’t fall out but will easily pull out if needed.
How skillful are you with a small drill because the proper engineering answer is to drill through the boss and axle and pin it with a bit of wire.
If you manage the hole then mix some 5 min epoxy to coat the wire as you push it it. Probably won't stick to the delrin but it'll stop the wire coming out