With that few dives, it might be prudent to configure your gear in a more "main-stream" manner. Rigging the inflator so you can't dump air is diverging pretty far from what I think most training would have to say about the issue. The pull dump is fine, the bungi might work, but you don't need to just add a ton of lead so you can descend fast, in the feet first position with some residual air in the BC. That suggestion kinda scares me a little.
If you want to sink feet first, you just need to dump all the air from your BC before you hit the water. If you exhale, wait a few moments for bubbles to exit the wetsuit, cross your ankles (it keeps you from unknowingly finning) then you should be able to sink from the surface at the start of the dive. The tank is full and almost 5 lbs heavier than it is at the end of the dive - assuming your weighting is pretty standard.