I have used an A19+6P (using 2 AAs) to power a P30 LA before. The length of three CR123 is the same as two AAs in series....with four A19 & the U2 body, I would have sufficent length for four AAs
If you're trying to save money by not having to buy 123's check out the vendor listing on the CPF Specials thread (sticky on the dealer's forum); some vendors have those for $1 or so.