Sooooo, here are my cutie girls reading and playing with their toys....
And this is what I do! If the baby gets fussy I put her in her Jumperoo or sometimes I stop and then finish exercising later (probably not ideal - but my kids come first).
I have never had a problem with having the computer on the book stand - it works really great actually! I also watch episodes of shows that I have missed (like LOST!!!) and sometimes even an instant Netflix movie!
It may not be the solution for everyone, but for me it is awesome! I really want to figure out a way to put the computer on the bike too.... (It has no book place.) I will let you know if I do!
(Oh, and I usually walk at about 3.5-3.8! - You may want to go slower at first, but unless you are typing - which I am NOT coordinated enough to do - you can actually go pretty fast!)