Yeah, I don't think the single bridge pieces will be lighter.
You could get a titanium bridge. I know I saw one similar to the stock fender ones. Looked pretty light. really expensive though. Google should find it.
Seperate bridges are probably heavier than a one-piece.
You're really not going to save a whole lot of weight though. A stock bridge isn't super heavy. Knobs, you'll only save a few grams. Plastic or wood would probably be lightest if you're okay with the looks. Pots really aren't heavy at all.
If you're going that crazy over weight, you might want to switch to smaller gauge strings and smaller frets.
Really, I don't think any of that stuff will help enough to make a difference. Light tuners can be good, but are more helpful for correcting balance, than actually making the bass noticeably lighter overall.
The body and neck wood is where most of the weight comes from. You could maybe get a bigger pickguard made up, and route the body down to a skeleton, leaving only the structurally important parts.
-Nick