The cable pull thing is no big deal, but I can't see the setup you're considering. If you want a lever at the end of the bar and another one by the stem, you're better off putting the regular lever at the end and the inline one at the stem.
Of course you can use a 26.0 lever with electrical tape, a strip of rubber, paper or whatever as a shim. No problem at all. I'd recommend Tektro rx2.0 or whatever it is called.
You just cut the housing at the appropriate spot, file it smooth, put end caps on, install the lever, thread the cable through. Brake and lever setup, etc. is covered in detail on sheldonbrown.com.
Oh, back to cable pull: inline levers are designed for cantis, which I feel need a similar amount of pull as V's; more than road calipers. You should be golden.