OTA and Raw Cable on Same Line

I don't think this is possible with the Roamio, but I thought I would ask. I have the Roamio basic with OTA or Cable option. I cancelled my cable this weekend, but I do see I still get quite a few SD channels coming in from my internet cable line. Of course, I don't get the local HD channels, which I do need. So, is it possible to use a filter like the LMP-450 for the cable line to have both the raw cable and OTA line going in from a splitter? I imagine my main issue even if this was possible would be the fact that I can not run a setup for both on the Tivo, but I thought I would just throw this out there.