I've used two old MTB's on my Kurt Kinetic trainer with great results. Rather than use a MTB wheel, I put an inexpensive (Performance Forte Titan) rear wheel on it with a Vittoria trainer tire. Since you don't need to use the brakes, it isn't important that the brake track doesn't line up with the pads.

From my spare parts bin I put drop bars, brake levers, and bar-end shifters (it was just a random mix of parts). Saddle was a random one I never got used to riding 100mi+ on, but works great for 60-75min at a time. Depending on your MTB gearing (44T big ring?), you are likely to spin out before the trainer provides enough resistance ... I bought the least expensive road double (52/39) square taper crankset I could find.

A cheap adjustable stem and tilting the front end of the bike up/down allowed me to get the exact same fit as on my roadbike. The bike as setup looks goofy, but it has worked great over the winters and I've gotten much more value out of the MTB frame than I could have by selling it.