Rifle Scopes Focal reducer / field flattener on a rifle scope

[doc187]

I have a clip on thermal but my rifle scope base mag is too high for the thermal to work well. Putting a lower mag scope on the rifle defeats the purpose of using the clip on as I want the rifle set up for long range. What I'd like to do is add a focal reducer to the scope for when I use the clip on. Is this a crazy idea and has it been done?