Your issue with IR will be there probably isn't line voltage in the box to power a "ir switch" like a spacer from lutron you get at lowes or similar supply chain. What you need is a dry contact relay type device. You do not want any voltage to bleed over to the millivolt system. There are several RF systems out, like above post, and you can customize your own set up. You just do not want to add or remove voltage to the existing set up, and a regular IR switch requires line voltage and will bleed. I have used a 110v controllable non dimming light switch controlled by a system, to activate a dry contact 110v Ac contact. So when 110 volts from switch is applied to the contact, it closes a set of dry contacts. This works very well, but I had access to line voltage, etc. this is an option though. If you have line voltage, get an IR spacer switch (do not dim) and proper relay and set it up. Otherwise maybe a google search finds specific options, as I am not aware of any other IR options. Good Luck and keep us posted.