The largest erogeonous zone is the brain. There are five senses to appeal to. I find coconut smell has a stimulating effect on me. Visually, squinting and giving him a nasty look might help. Reach down and feel his "swimmer muscles" while he's doing it. Don't fake it but by all means exaggerate certain things, like how hard you hold him when it feels good, the noises you make will encourage him. You can also do it sideways. Always helped me.
Precious and fragile things
Need special handling
My god, what have we done to you?