Large recordsize is your friend here. If you set recordsize=1M on the dataset you’re torrenting to, there’s no need to bother with a staging directory followed by a brute-force copy.
There is essentially no difference between “maximally fragmented data, but all fragments are 1MiB or larger” and “unfragmented data” in terms of storage performance or load, on a general-purpose filesystem (as opposed to something laser-focused like a tape drive).