As long as the velcro ends up between the tube and the brake wire, you're probably ok.

I think that there are a lot of variations, based on bike frame size and positioning (clearance below and above stoker stem), possible.

I've been considering:
- small cylindrical handlebar bag (5" or so diameter, 8" or so long): can hang from stoker's bars, and not so wide as to be bumped by knees;
- Bento-styled bag, with custom stabilizer up to the stoker stem, so stoker doesn't have to reach way forward / way under captain's saddle;
- something thin and triangular, like the Nashbar "slice" bag, to mount atop the stoker's bar/stem intersection (zippers on "slice" are oriented the wrong way, however - for 'normal' bar/stem placement)

I think that ultimately I'll customize something -- after all, the waterproof vinyl fabric and zipper stock which I picked up at http://www.seattlefabrics.com/ was for bike bags -- with a couple of mesh outside pockets, shaped sort of like an under-seat bag, and tied off (velcro?) to top tube, stoker stem and stoker bars, extending maybe 3 or 4" behind the bars. I've mocked up a couple of paper samples, guess I need to get the sewing machine out and start the fabrication process.

For small pocket cameras, the slickest arrangement I've seen yet was by one of the Evergreen Tandem Club stokers: a loop of nylon line pinned at one hip and looped over the opposite shoulder, with the camera's short "leash" passing through the loop (or, with a mini-carabiner). To use the camera, just slide it up out of the back jersey pocket nearest the pinned hip (reach around behind one's back), bring it up to look through viewfinder or at the screen, snap the pictures, and then stow it. No worries about dropping the camera, and enough "stretch" in the restraint system to easily handle it.