Modification: While the method below largely worked, there were some areas between toes that didn't shape well, that is they dried in a way that didn't fit my feet and had to be broken in. Next time I do this I''ll line the toes with veggie-bag and wear them for a while so they shape right as the Freesole dries.
I have two pairs of VFF that I needed to coat between the toes with Freesole. One because a previous coating was wearing out, and on that pair the heels needed a coat as well, getting some miles on them. The other pair is new, unworn outside yet: From now on I'm reinforcing the cloth between the toes before I start hiking in any VFF. If you hike in any place with small gravel and dirt, they will get in caught between the toes and grind holes in the fabric. The Freesole takes the punishment and is easily renewable, even easier now.
The previous way to do this was stuff some grocery bag in the toes and then clamp an unstuffed one out of the way and work on the exposed sides of the adjacent toes, wait until it dries, then clamp the next one and do those sides. The AV Aquaseal dries quickly, but reportedly wears faster. Freesole is an overnight cure. So clamping and gluing adjacent toes and covering all 8 sides took time.
Being impatient, I tried something else, and it largely worked.
First, stuffing the toes is optional, there are pluses and minus to it, moderate stuffing is best IMO. Depending upon how your VFF fit, which toe pushes out where and so forth, overstuffing can make things less comfy. This one is up to your own observations. The two largest toes are the only one's I've bothered with.
Next, have a tube of Freesole or your chosen glop ready, as well as some of those fruit and veg bags from the supermarket. You need 8 pieces of a bag for a pair, you can tear them or cut them out, but you need about 3" squares, roughly, doesn't matter exactly, as long as they are larger than the area between the toes. These are the clear thin bags that tear easily and don't hold a lot of weight. Freesole doesn't stick to the ones I have. Next get some glop flowing and coat between all the toes of both shoes. I coat it all, Spyridons have overly flexible fabric between the toes that loves to harbor visiting rocks and then develop holes.
When you're done applying and have your fingers clean or your gloves off, slide a piece of veg-bag between each set of toes, right in to the hilt. I let them sit in a place with airflow on a disposable surface like an advertising flyer, in case they stick.
The next day, pull the little sheets out, done. Go out there and explore.