I was able to use geometry nodes to do some placement, but after quite a bit of effort, it still looks pretty bad. I think it especially looks out of place since it's not lightmapped. I think I'll abandon this endeavor and just settle for a retexturing I was doing separately.
Thank you for the offer! I actually already had some mossy retextures that I was doing for the bark and soil, though. My hope was to add some geometry for moss on top of the retexture. But I think I'm okay with giving up on that at this point :)