How about dry tek (mimosa and calcium hydroxide) + acetone pull, then salting with FASA. Fumarates should precipitate, but then again all the impurities in acetone might make that a problem and not precipitate well.
In any case if it doesnt precipitate, evaporate the whole thing, wash with acetone, re-base by making wet paste with calcium hydroxide and letting it dry, repull with acetone, re-salt, then hopefully now the fumarates are precipitating cleaner? When they are reasonably clean/tan fumarates, redissolve in water, add sodium carbonate saturated solution and let freebase crystalize in the fridge.
One thing about the first step of all this, the mimosa+calcium hydroxide, is that if its wet, the acetone will mix with water and if you separate that, you will have some mimosaimpurities+calcium hydroxide+alkaloids. So would be better to evap all of that and then pull again with acetone, before continuing to the salting part.
All of this is theoretical, try it out and let us know if it works