Before you drill let me check to see if my pocket jumpstarter will charge off the OEM USB..
UPDATE
I can report that the OEM USB port in the left saddlebag will charge a WinPlus jumpstarter rated at 8000 mAh (3.7v) 2700 mAh (12v)
I can't tell what the charge rate will be but I imagine it'll at least keep a device topped up while driving.
I hope this helps somewhat.
Happy trails..