Does the Aqualung Wave have somewhere to attach a 2 inch crotch strap? (something like a plastic backplate with the usual slots like a wing's, like some other jackets have)
Yes, sort of.
If you lay the Wave down, with the back pad facing you, you will note that the bottom of the pad can be pulled up by separating a velcro strap that holds the bottom in place, attached to the plastic 'spine' / backplate. There are two possible points of attachment of a crotch strap to this plate:
1. There is a 1 inch slot, #1 in the picture below (that the velcro strap on the backpad was slipped through), which can be used as the anchor point of a 1" crotch strap.
2. There is a hole above that, #2 in the picture below, through which a small SS bolt can be run, to which a 2" crotch strap can be attached.
3. The front of the crotch strap can then be sewn into a large loop, which will slip over the waist strap (not the cumberbund, but the strap with the buckle) as the front attachment point.
4. Or, if you want to make a 'Y' strap, with the bottom of the 'Y' attached to the rear of the unit, as described above, the ends of the top of the 'Y' can be run through the base of each of the shoulder straps (#3 in the picture, below). I don't recommend this approach, merely pointing out that it can be done.