Where do you live / what is the climate like? The warmer the location the more challenging this will be.

What is the reason you're thinking of trying this, are you experiencing problems with rot? Personally I think they perform better with at least little bit of organic material in their mix but that's just my opinion. Several folks on this forum have gone with all gritty mix for theirs and most have either gone back to their regular medium or have amended the gritty to have some organics in there.

Also, with one small plant it won't be an issue but with many plants or a very large tree (think 4 years!) you're looking at a lot of pumice ($$) and that tends to be quite heavy especially if moving the plant in and out for winter.

I look forward to hearing more advice from other members and please keep us posted!

I live in USDA Zone 9b (SF Bay Area), Sunset zone 17. I wanted to pot the plumeria in a medium that is fast-draining and dries quickly so that I can fertilize more often (is my thinking wrong on that one?). It will be indoors over the winter in a grow tent, with ambient temperatures between 60 and 85 degrees, roughly. What mix would you recommend if not the gritty mix or pure pumice?

I would just be careful about over fertilizing because it can cause problems for the plant - if the growth is too fast the limbs are weak and can't support their own weight, your plant could look lanky, salt build up in the soils, etc.

That having been said you can certainly do a diluted feed on a more regular basis - someone else can possibly comment on how much is too much or I've also heard of people calling DynaGro for specific info. (I use DG FP also, love the stuff)

I would lean towards something in between for your soil mix - potting soil mixed with pumice or perlite would probably make your plumeria extremely happy and create a very well draining mix. 60/40 (pumice/soil), 70/30, maybe 80/20 if you want to go very lean, something in that range? There's no just one right way to do it, experiment and see what works for you to reach your desired outcome.

You very well may be able to grow a nice plumeria in pure pumice but to do it to fertilize more frequently I would have to ask what the desired outcome is of feeding more frequently? Because depending on that and how much you want to water (in the summer I don't know if you could water enough to keep the plant hydrated in 85+ temps) you could achieve a very healthy plant with less work and cost if you wanted to, it just depends on your goal and situation.