I've been thinking for a while about how to make a pump-mag with an autotrigger. The key to doing this would seem to be to find a mechanism that would interrupt the direct linkage that currently exists between the trigger and the sear. That way, when the trigger is pulled, it doesn't hold the sear "open" but allows the sear to toggle with the pump stroke. If the gun has been pumped, then it fires immediately upon a trigger pull. Otherwise, it waits and then trips the sear each time you pump.
So enough theory: I think I've got a way to do it. I've modified the following graphic to show how I think it would be done. It should be pretty self-explanatory, but I'll add a few notes:
-The telescoping trigger rod and spring combo make up the mechanism that allows the gun to operate with an autotrigger.
-The pump rod could reset the sear in any number of ways, but I've got another pic I'll post that shows how it might be done with a simple modification of the existing pump kits.