My guess would be to make a new model that is just the particle effects and make it so that it'll hang at the right place
Best way to do that would be to remove the animations of the Burning Archer (Transfer over animations of a barrel or something), then use my nifty empty geoset which is actually Whitehorn's anyway to replace the geosets, then you'll just have the particles.
Might take a bit of time after that to remove the unneeded ones and move the needed ones around, but it should work in the end
I'll did up the empty geoset