Keep USB slots powered when PC is idle

Anyway to keep my USB slots powered when I close the lid, or set it in hibernate?

Have you tried disabling selective suspend for the USB in advanced power settings?

Selective Suspend will not work when trying to charge devices via USB. A computer's ACPI is designed to restrict that much power to USB ports when sleeping and shuts down everything when hibernating.

Unless your computer has something specific that's usually referred to as "Sleep-and-Charge" [common in Toshibas and netbooks] you're out of luck.