If you know what kind of hitch it is, find a shop that installs them and get a cut-out piece. A body shop should be able to easily weld it in place good enough to cover with the liner. Maybe throw a few pieces underneath for support and you're good to go.
Any decent welding shop should be able to provide you with a suitable patch panel - simply prepare it with a good anti-rust covering on both sides, such as Rustoleum - apply a common sealant around the edges for weatherproofing, and use stainless sheetmetal screws to secure it in place.
If you know what kind of hitch it is, find a shop that installs them and get a cut-out piece. A body shop should be able to easily weld it in place good enough to cover with the liner. Maybe throw a few pieces underneath for support and you're good to go.
I like this one. The primary difficulty, of course, is bridging the kerf. I assume a TIG welder could provide the necessary fill.
Ryan