[CapnBFG]

Thanks for the advice.

Getting a second PIC to be the I2C master is what we decided to do. We ordered this eval board yesterday:
http://microchip.com/stellent/idcplg...&part=DM163022

That has an 18F452 onboard already and comes with a 16F877 in addition. We chose that board because the manufacturer of our ultrasonic rangefinder shows both of those as examples on their website and provides sample code for each.