Here's a link to a potential option. 3M scotchguard is what I use. cut it to size and stick it on after making sure the paint is clean. It will come off nicely down the road if you heat it up.
3M makes clear vinyl, you could put a sheet of it in the area. It's mostly inconspicuous and I assume can hold up to a little gas. https://www.amazon.com/Scotchgard-Clear-Paint-Protection-60-inches/dp/B004VG8DS0
People use it on their hoods for rock chips, etc. I don't see why it wouldn't work.
These will be super helpful for next time... I cut mine by hand recently.
I used this $20 6" roll of PPF from Amazon that accommodates them nicely: https://www.amazon.com/gp/product/B004VG8DS0
You might consider 3M Clear Protection Film. It was easy to trim/apply and it's hardly noticeable.
This is really common on a lot of bike brands, not just trek, and not just ones with internal routing. Every bike I've ever owned suffered from this growing up. I was smarter with my last bike purchase and bought a couple rolls of 3M Scotchgard Clear Paint Protection Vinyl Film in 6" and 12" sizes and spend a day patiently making templates and cutting the stuff to fit, and wrapped nearly the whole frame/fork. I ride mountain bike trails so I get rock dings in the downtube and rubs on the toptube from my bike rack. I ended up putting 3M Safety-Walk Slip Resistant Tape on the undersides of those tubes for extra protection. All in all it cost less than ridewrap but took some time. If you only wanted to put a couple small pieces around your frame where things rub it would only take a few minutes and cost a couple bucks but it's well worth it, you just have to be patient and use a hairdryer and slightly stretch it when you put it on, and it goes on invisible. Photo: First bike fully wrapped Photo: Starting the second bike.