3 years old can go off feed for MONTHS, assuming he has a good body weight (you did not answer that) he will be fine, sexually mature individuals tend to that.
Now heat is around 85 what is it EXACTLY? (Around can mean anything) What is it on the cool side, on the warm side, where do you take your reading? What type of thermother do you use? (answering my other questions would help too (all of them)
You do not assist or force feed an animal unless his health is in jeopardy and he has lost a tremendous amount of weight.
Right now you need to concentrate on the scale rot, by treating the animal and by addressing your husbandry.
As for feeding if YOUR husbandry is optimal and once treatment is over your BP will resume feeding.
Now if his health his at stake than your VET should be able to assist feed your BP however I seriously doubt it is a necessary action.