Yes you can, but I believe water will cause the powder to lose potency over time. So if you try to mix a batch in a vial I believe the potency will start to deteriorate in as little time as a week or so. I would suggest using something like grain alcohol, propylene glycol or similiar liquid if plan on not using the whole mixture within a couple of days.
Also, as mentioned previously you cannot preload the gellcaps as they will dissolve from the liquid. You would have to swallow them soon after loading them.