My thoughts are that you should go ahead and ask your T for the favor. A favor generally is something one asks of another that is above and beyond what is normally expected of someone. Perhaps you want to ask your T to attend a concert where you are playing the piano. It is outside the scope of therapy for him to attend, but then, that is where the "favor" comes in. It can be therapeutic for the client to have their T there to cheer them on, to provide support and maybe even to be proud of them. Perhaps the client needs this kind of support from T to help them feel better about themselves. It's just an example. I don't see the harm in asking T and think you should ask. However, you need to be prepared if T says "no". It will be very disappointing and you will need to still carry on and play at the concert. By the same token, if T says "yes" how wonderful would that be? It's a gamble but I'd say to take the chance. Just be ready to carry out your mission without T if he says no, O.K.? All the best.