I know its not popular around here, but I would bring-in for the full bet. The last thing you want here is the usual flock of limpers you get at 2/4, and the main point of limping is to reraise. At this level, too many pots are unraised for this to work well in my opinion.

Fifth could well be a fold - it appears that he's picked up a pair of kings to go with his jacks, leaving you two outs in a not very large pot.