Just take a 2 way splitter and reverse it. Connect the OTA signal to one of the ports and a modulated signal to the second. The input port goes to the input port of the distribution splitters going to the rest of the TV's in the house.
It has worked every time that I've installed this way.
I have heard of people doing it that way and I have heard that it works every time, but I've been told that they do not last? The tech's I spoke to said that you would get a service call in about 6 months? Not on everyone but on some of them. Have yours worked for over 1 year on all installs? Also do you know if it would work with the modulated output of the second tuner and a Cable Modem signal?