I def think it would be worth asking him to go with you. If you asked him in person, I don't think that would be putting him on the spot at all. I assume he would have to miss work to do this, so I would offer to pay him for his time. I guess if he doesn't have to miss work, I would hold off on making the offer to pay him. It sounds like he wants to support you. If he cannot go with you due to ethics, client load, previous commitment, maybe knowing the "no" isn't personal won't be so hurtful??