Actually the slotted tungsten beads do work on the 90 degree hooks. Just put them on with the slot facing forward. Somewhat tricky on smaller hooks, but should be fine on the sizes you are using. Which hook did you settle on?

Another trick is to use the "pin" method that Phil Rowley advocates. Put a brass/tungsten bead on a sewing pin (I like brass ones that do not corrode), bind it down on top of the hook over the eye such that the hook will ride balanced, and then tie the rest of the fly. This method works quite well, but you needs to find some stout pins if you use this in moving water, because the sewing pins will shear off on rocks. I've been trying to find some stouter pins for a while, so let me know if you find some.

The lowest tech solution is to just crimp a splitshot of the appropriate weight on the end of the hook. If it falls off, just crimp on another.

Finally, Do-It Molds makes mold kits (http://www.do-itmolds.com/), so if you really want to start playing with molten heavy metals, they already have an off the shelf solution, or even blank molds if you really needs something custom (doubtful).

Jigs have been popular in the PNW for steelhead for quite some time, but they are just starting to make inroads elsewhere in fly fishing. Post your results when you find a solution, and good luck.