Can I cut off the 5v output of the IOIO to the Android?
USB doesn't have the notion of TX and RX lines, it's not a UART. The data lines are D+ and D- used for bidirectional differential signaling.
The VBUS line (which you refer to as Vcc) is essential for detection the presence of the host (IOIO in this case), so what you're suggesting will not work.
The best you can do is use the current limiting trimmer that's on the IOIO. Start with it fully clockwise, then, with the Android connected, turn it counter-clockwise until the connection drops, then back some.
The minimum current that can be achieved like that varies by phone model.
Also, turning the screen and comms off on the Android will reduce current significantly provided the phone battery is fully charged.

Hint: in the future, you're most likely to find answers to IOIO-related questions on the ioio-users Google group.