If there's an outside wall where you want the TiVo box, they can come in through there and fit a wallplate. Then theres coax from wall plate to TiVo. Its usually a neat job. You would be better getting a TiVo at each TV you want to watch your VM package from, as that's a far easier solution than mucking around with long HDMI leads or dubious quality video senders and the like., £5 a month extra for a 2nd box.
The issue with an IRS install is you're distributing the RF signal. So whilst in theory you could distribute the VM signal the TiVo needs that way, the major stumbling block is VM use a different spec of coax and wont connect to anything you have installed already*
But you'll still need a TiVo at each point that way because you need a STB to convert the VM RF signal to a TV picture.
*some engineers will , but they're not supposed to.