30 pin y cable? Need to charge and use the 30 pin port

I use a app called jamup to play guitar through. The interface uses the 30 pin port. Problem is I play club gigs that are 3- 4 hours long and the ipad can't be sleeping as I need to change presets etc. often. This drains the battery quickly. So I need to connect to a charger. Problem is just 1 port.

Any thoughts on how I can resolve this? I need to do two things through the 30 pin port. Charge the iphone/ipad while using a interface that also needs to use that 30 pin port. Search for a 30 pin y cable isn't pulling up anything so my fear is that is not made or wouldn't work and I'd need some other option.

Looking for something with a very small footprint and very quick and easy to setup. Not doing this at home. Running off from work to a club gig and quick setup, play for 3 - 4 hours, pack up and go home real late at night.

Dave