It seems not much is dissolving but it is.
1g fumaric acid dissolves in a little bit less than 100ml of acetone (
source)
Freebase DMT molecular weight is 188.269. Fumaric acid weight is 116.07. DMT fumarate has a molecular weight of 492.608 (DMT + fumaric acid + DMT)
That means fumaric acid is around 38% of the weight of DMT fumarate. So 100ml FASA should be enough to salt out more than 2.6g DMT.
Do you still think you will need too much acetone to dissolve your pile?
As for putting fumaric acid directly, it's probably not a good idea as Mindlusion already explained elsewhere. Fumaric acid is a diprotic acid, but due to equilibrium, if you add too much fumaric acid at once it may theoretically form a monoprotonated salt. Generally these salts do not store well, being hygroscopic, do not crystallize easily and can degrade.
So you want to do FASA the right way.
Or... You can do partly the right way and partly the wrong way, and then see what happens and let us know the results