I think that a 90 degree would be better. If you didn't notice, the 45 bend is actually a wider angle than 90 bend...those crazy PVC people.
Okay, here it is. It's simple, but it should work.
You need a 90 degree bend, two pieces of PVC, and two end caps (CPVC would work too as long as you can get all of the above). You'll also need a drill.
Drill a small whole in each endcap. To make this really simple, just get a piece of string. Put it through all the pieces of the bipod, as shown above, and tie just outside the end caps. Make sure that the string has enough slack that you can take both legs off of the 90 bend. If you don't want them to dangle, you could make some kind of strap to hold them against the LBB's body when not in use. Then just undo the strap and press the pieces of PVC into the 90 bend.
Alternatively, you could replace the string with rubber bands or a bungee cord of some sort. If you do this, then (I think this will work) as soon as you loosen the strap the bipod will sort of pull itself together. The bad thing is you'll need a stronger strap to hold the bipod legs back.
A tip for length: make sure the height of the bipod is greater than the length of the grip, or you won't be able to elevate the LBB (since the grip will hit the ground). Note that the bipod height will be less than the length of the PVC legs, since they're angled.
