He can't participate in a semi-aroused state, after all!
Ummmmmm hate to say this, but some can participate that way HP. My H does almost everytime we have sex, which is about once every 2 months. If you remember he has ED problems and he gets semi-hard and even is able to partially penetrate if I keep really still. (not much fun for me) Its not real fun giving a BJ either to someone who is only semi hard, its really hard to tell if they are enjoying it or not