There is a HUGE market for peds psychiatrists pretty much anywhere I've ever heard of. If it's income you're looking for, the most obvious thing to do would seem to be to pick up some peds psych outpatient work? You could do this on your own, if you wanted, just setting a rate and taking cash-only. As long as you felt comfortable with your current skill set here, of course.
I know people who triple boarded, but they mostly do peds psych. They just tend to attract a patient load heavy in the more medically complex kids - kids with a high physical disability load, Sz disorders, PDD, etc. I don't know anyone who is peds psych boarded but does some pure peds patients. Partly, the overall total demand and the reimbursement as well are both so much lower for straight peds that you'd have to have a pretty strong reason to be wanting to do it rather than something that's one of the biggest shortage areas in medicine.