Yeah. I get it. Especially if he's gone to the trouble to bury it in conduit already.

Personally, I think I'd still use the existing cable as a pull string to pull a piece of fiber through By the time you spend ~$70 each on two repeaters plus the cost of something to inject power, you're at roughly same price and you still have a bit of a kludge.

Also, make sure you get the grounding right, or you'll have some toasty equipment if you get nearby lightning strikes.

Good luck. Let us know if it works.