There is no oil pressure, per-se, against the valve cover - only a slight vacuum from the PCV system (at times, maybe a slight positive pressure). Most valve covers leak (with a compromised gasket) at the lower side just from pooled oil and gravity - not from oil or crankcase air pressure.
Would you say that there us a gouge or nick in the mating surface, but other than that, the entire mating surface is a perfectly straight line (no warpage/bowing)? If so, you could probably do fine by cleaning up any raised parts of the gouged area with a file (jeweler's file would be preferable) being very careful not to disturb any nearby (undamaged) mating surface, and then filling (over-filling) the gouge with J-B Weld, then, after it thoroughly cures, filing/sanding the excess J-B Weld down to be exactly flush and straight with the rest of the mating surface. I believe the gasket inserts in a groove in the bottom of the valve cover, so also clean up any gouging inside that groove by, again, filing any raised metal flush and filling in any gouge with the J-B Weld, then file/sand flush.
The idea is to re-create the original shape (maintaining overall straightness) of the mating surface and groove as closely as possible.
The gaskets for the valve covers are high-quality and very pliable silicone rubber and should seal against remaining minor surface imperfections, but it wouldn't hurt to add a thin layer of black RTV to the damaged/repaired area when re-assembling.
Of course, thoroughly rinse out the repaired valve cover with brake parts cleaner - you don't want to be introducing any metal and epoxy filings into the engine.
. . . or find a used valve cover.