I did the same thing a while back, but for slightly different reasons. My ONT has always been under my house in the crawlspace wired via CAT5e to my router (Unifi USG) in the house. Originally, the ONT was plugged directly into power via an outlet i installed under the house, but I wanted it to have UPS support. Since I already had a UPS for all my in-house equipment, I didn't want to add another one in the crawlspace. So I bought this TP Link POE splitter https://www.amazon.com/gp/product/B003CFATQK/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
and used one of the many extra POE injectors I had around from other Unifi hardware (most is powered through a POE switch). I had to find some barrel plug adapters for it which was actually the hardest part of the process. But it works great. Also makes it easy to power cycle the ONT without going in to my crawlspace.