How about answering "Sorry, I don't have time to fix this over the phone, but how about you invite us to dinner and I'll look at your computer then?"
I have a super-helpful computer-techy dh too... But he's getting better at asking for help himself for other things, and making a point about how it's great to "trade knowledge". Or asking if they've already called support (they never have, but at least it plants the idea that it's possible).
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett