Are you experienced in PE? If so, I’d try pumping or clamping.
Gain only in girth seems highly unlikely. You’ll probably gain some length too since most methods of PE seem to have that synergistic effect (clamping maybe the least though). Gaining 1” in girth will be insanely difficult, but perhaps not impossible. Although, I’ve personally only stumbled across one person gaining that much girth who was also believable.