No reason to think it wouldn't work, yet one needs to try a few things before he jumps to extractions.
1) make sure that addition of FASA in pure clean DCM does NOT cause precipitation of the fumaric acid
per se.
2) make a test run, e.g. dissolve some freebase spice in DCM and try to see whether it salts out nicely with FASA.
Then one would be ready to go ahead!
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