Slew rate limiting of bidirectional lines
If you wanted to block higher frequencies you could use an SMT inductor to limit the current. I've used them before in the place of RC filters to limit current into a cable that connected to processors on a SPI bus. 

Because the cable was built wrong in the first place when I was asked to upgrade the digital logic, the cable had too much mutual inductance between conductors and a rising edge on the MOSI in one conductor would cause a runt on the MISO in the conductor next to it. Tried RC filters but they were too slow, so I blocked it with a 0.1uH chip inductor which slowed down the rise time enough to stop most of the cross coupling. Something like this might work in your case.