Dave de Vos
At 0:43 http://www.youtube.com/watch?v=7wV49Q9mpUI
shows a variation of the forward roll from seated position (the front arm going outside instead of inside). (BTW, the instructor in this video is also a member of AikiWeb, Chris Hein)
I had no idea that video was from one of the AikiWeb members! That's the one I used when I first started Aikido, before I found AikiWeb. Great video, it really gave me a lot of confidence!
Although I see nothing wrong with doing some weight lifting. Just remember that your goal isn't to gain bulk, but to tone up, so make sure to stick to using lifting exercises where you can comfortably do 3 sets of 15, instead of 3 sets of 10 at the heavier weight.