Since the spots are NOT on soft tissue, you can use an actual physical barrier rather than an ointment or cream. I use liquid bandaid. It should last for a 60 mile ride, but take the cream/ointment of your choice just in case it doesn't. I sometimes use a blow dryer on low to speed up the drying. I also sometimes use actual bandaids that are marked as durable and water resistant. Apply them to dry, oil free skin, and they will stay on. I have tried blister bandaids, but they are more expensive and don't stay on any better.
Grits
2010 Trek 5.2 Madone WSD, SI Diva Gel Flow
2002 Terry Classic, Terry Liberator