Overview
You can do a double weapon jump!
How to do it
Jump to a falling weapon. When you pick it up, you do a regular weapon jump. Now, throw the weapon and jump at the same time. In this video, I jump to it, weapon jump (normal), turn around, and throw the gun and jump after. Notice the jumping particles (white particles going UP), happens twice.
Note: Doing a weapon jump while holding a weapon is still possible. It doesn’t matter if you’re holding a gun or not.
Juggling
When you do the weapon jump, try aiming up. Sometimes, the gun will fly upward, sometimes it doesn’t move very much. When it doesn’t move much, you can move to it and do it again. Or, if it flies up, but not too fast, you can go up with it. In this video I show both, though for the first one, the gun moved down quite a bit before I could catch it.
In this one I shoot the rockets for a little extra upward momentum.