I used a blow-dryer when I bathed their bums recently, and they didn't mind it, most liked it once they felt it was warm air. I had gotten them pretty wet in this first bath, leg and even belly feathers too on Butters who had a bad case of stuck-on poo back there, and I didn't want them getting chilled. I used sweeping motions while fluffing with my fingers and I could monitor how warm it was (switched to cool for a bit, then back to warm, closer and further away, just like the salon!). For some reason everybody stood there on the towel relatively serenely once they felt the warm air.
I also used a little coconut oil around their vents and a small bit on the feather shafts there while the feathers were wet, in the idea it would help replace any oils lost in the bath, and help poo fall away later. It warms and thins, and didn't prevent any fluffing; your fingers are distributing it I guess too. I made sure to start the blower up a good 6 feet from them to not startle them (I stepped away with it and held my arm away) before bringing it closer.