It's easier to convert it to the phosphate salt. 85% food grade phosphoric acid is sold in hydroponic shops as a pH lowering agent. You just dissolve the freebase in IPA or acetone and add an equimolar amount of the acid with rapid stirring. An equimolar amount should be about half the weight of the 2C-E used. The crystals quickly start to precipitate and it forms a milky looking slurry. You then filter the crystals out and wash them with some more IPA or acetone, in case there's any extra acid (which will not evaporate because it's a high boiling point syrup) and dry the filter cake. It's more soluble in water than the HCL but practically insoluble in alcohol. It'll be somewhat less potent though because the phospate part is heavier than the HCL. You'll have to calculate what the exact difference is because I can't recall. Probably about 3/4 the potency, something like that.
Here's something else you may find interesting. I was going to post it in a 2C-E thread but couldn't find one so I guess this is close enough. Having read that the unpleasant effects of PEAs are due to its adrenergic effects I did a search for natural antiadrenergics and found one called Motherwort. I bought some tincture of it and took 40 drops of it and a low dose of 2C-E phosphate as a test. It was about 15 mg total which I took in two doses of about 8 mg each, because I didn't feel much 90 minutes after the first 8 mg. I also took another 10 drops of the tincture when I took the second dose. I had just eaten a meal before I took the second dose because I got hungry, so that may have had some effect on me not getting all that high.
Anyway, I still didn't get real high but I did get pretty stimulated and had slight hints of visuals. The important point being that there was no nausea whatsoever and no muscle tremors either. I did get some tingly feelings kind of like with ephedrine but that was all. I didn't use an NBOME for the test because I was out of cut NBOME and it's a pain to make more up.
So it appears that motherwort may indeed eliminate the nasty side effects of PEAs while leaving the stimulating part, though admittedly this was a low dose. Still, even that low a dose made me quite nauseous before. It may actually be cutting out much of the high too, hard to tell with the low dose. I did feel pretty good though, like just enough LSD to notice it.