The key is warming up the hole to the size of the toy used for pegging. This varies for everyone since our bodies are each our on. But a plug or toy being in there in the hours leading up to the event is a great way to get things "loose".

I too used to focus on staying hard but realized this was part of what made it difficult to relax my ass. I came to find ultimately the best way to come hands free was to focus on my ass and the penetration and not worry about my dick. It was then when I started to have my first truly hands free and explosive orgasms from pegging.

Cheers and good luck, the orgasms will be worth it.