Convert OTA to Cablecard?

I bought my Roamio OTA with lifetime last year, and I love the EPG and ease of use, but my OTA antenna gets pretty spotty reception (I'm about 46 miles from major towers). I'm a cheapo who generally only watches the basic networks, so I'm reconsidering a basic cable package, has anyone successfully converted an OTA box to cablecard? I remember some talk of this about 8 mos ago, but didn't follow it, as I was optomistic re dialing in my OTA. I"m in north san Diego, almost halfway between SD and LA stations, so I sit on the cusp. Charger season is approaching, so need to stabilize my signal.

Thanx,
Joel