I've done this. My employer likes me to stay legal, so I looked up the FCC rules about
unlicensed operation (I'm in the US), did the calculations, and determined that I
could in fact keep the leakage below limits, and the input power to the HS and BTS
receivers within proper range. I'm using the BTS at minimum power of course. I use a
Minicircuits ZAPD-20-S+ power splitter, which has 30db isolation between the two ports,
and a single 30db attenuator on the HS side. With my equipment I need a minimum of 24db
attenuation between each transmitter and the opposite receiver. I did not check the
leakage as I don't have a calibrated field strength meter but according to specs it
should be ok. I've got the numbers if you're interested.