Have you tried putting a generous dod of said lotion on a long length of fabric, dangling it behind your head with one hand, reaching behind you and grasping said fabric (a towel, maybe?) with the other hand and then manoeuvring said length behind you so that said dod is near to offending parts, to which said dod of said lotion may be pressed by appropriate manoeuvres of said fabric?
Or, more simply, put a blob on the floor and roll on it!