An inline Low Drop Out 3.3V voltage regulator between the CC3D and the BMP180
But... I'm pretty sure that is functionally deprecated code, requires code changes and building it locally, and doesn't have any flight modes that use it in the CC3D.
We all want to use our old hardware, but by all counts, this is a task best performed by buying a Revo class FC that has baro built in and has a working baro driver and baro flight modes (Altitude Hold and Altitude Vario).