The 5-MeO-group does not change any reactivity regarding salt conversion. Actually, it is even quite unreactive to anything. You have to use quite nasty chemicals to cut that group off from the molecule ...
So by simply adjusting the molar mass you can just proceed as you would. Keep in mind to slowly mix any acidic solution with your 5-MeO-solution as otherwise (upon very fast mixing) you may drop your 5-MeO in another molar ratio and this may let some 5-MeO stay freebased in the solution.
This may happen with acids with 2 protons like citric acid, fumaric acid, malonic acid, but you should still use them, as they are the only one to produce resistant salts which do not collect moisture from air. Just dont throw everything together at once and you will be safe.
EDIT/PS: Actually it may not be even better to convert it to the salt form, if you seek to insufflate it.
I guess your aim is to create a water soluble form, which would in theory be taken up in the nasal system much faster compared to an unpolar compound. Very often I read here on the Nexus that a lot of other compounds show a LOWER activity when applied as the salt form, for example bufotenine - which seems to be much weaker when applied as the salt, so weak that you are definetly required to use the freebase.
That may be due to the fact that indeed a salted ionized molecule is dissolved nearly instantly in the nasal mucus and may then be absorbed into the capillary system of your nose. But on the other hand the pharmacodynamics of the drug may require a step where a transport through membranes will take place. And this is heavily slowed down for ionized molecules. And this may be the reason why a lot of drugs should be administered as the freebase in order to actually increase the uptake speed. As Bufotenine (5-OH-DMT) is quite similar to 5-MeO it may actually be the same case for 5-MeO. Maybe keep a tiny portion of 5-MeO as the freebase, then when you have both ready you may insufflate a tiny portion which would just be above the minimal dosage required for a noticable effect - while measuring time. Then you would know if any of these both forms is less effective regarding potency and based on other substances it may actually be the salted form