What I have been doing for having the dmt+harmala salt combo for oral ingestion, is measure an amount of freebase harmalas (such as, say, 1g), redissolve in warm vinegar, and saturate with salt to precipitate the hcl salts. The resulting precipitation has plenty of salt contamination, but thats perfectly food safe, and you anyways just divide the precipitation in the according number of doses thinking of the freebase weight, so if it was 1g, dividing in 5 doses would be appropriate. Then I just put that in a couple of capsules together with dmt fumarate and thats a very practical pharma ingestion method. I get no nausea this way, and dont feel any of the taste.
BTW, where did you see that harmalas dont dissolve in limonene? If I remember correctly, they did dissolve but the issue was the formation of harmala red in limonene. I might be wrong though. Another thing is, even if harmalas redissolved in limonene and didnt create harmala red, it wont necessarily salt out with FASI (for example mescaline fumarate is soluble in limonene, so FASI wouldnt work with it.. For harmalas, we have to test this to know). And FASW would still have fumaric acid excess in any case, just like your proposed method, so might as well do what you are mentioning if you dont mind.
Another idea would be to, instead of making a random amount of fumaric acid water solution (or FASW) and redissolving the harmalas as you proposed, would be to make a molar calculation to have just the exact amount (or a tiny bit more) of fumaric acid to attach to the harmala molecules, and then evap that, to not have any excess fumaric acid. The problem is, I dont know if harmine and harmaline fumarates are 1:1 molecule of harmala:fumarate, or if its like 2:1 (like dmt fumarate is), or 1:2, or what... So this would have to be known before being able to make the molar calculation, so maybe some of our chem experts will know.
Im sure there are other clever ways we can think of, the problem is im not at home for the next couple of months so I dont have my harmalas to test, but if I can think of anything else, I can suggest here and you test for us if you want