Just last year I came up with the idea of using a thong as a base layer and snugging it up by tying it up in the back at the T. Figuring out how
to cut and tie it was the hard part and I'm still working on 'perfecting' it. My disclaimer is that I am not like that Asian guy they call Hung Lo so I can fit into some smaller spaces. But you might consider trying this out - especially if you need to tuck wearing a narrow piece of costume between your legs.
I use the closest to skin color Vanity Fair Illumination Thong
for this and it works really well. After tying it off to what I think is snug enough to hold everything in place I cut off the excess string from the knots and use Loctite brand Vinyl, Fabric & Plastic Flexible Adhesive
to keep the knots from coming loose.
I'm not sure how to describe how effective this was for me but I was able to do high kicks with nothing but Vanity Fair Illumination Helenca
panties over it and never missed a beat! I also tried the splits but never made it down that far. (I usually don't wear lace panties but I was at a wilder party that night)
One tip to tucking is to lube up with a good skin lotion to help everything slide into place. I've found it makes it much more comfortable and smooths out the operation.
If you email me I will email you a picture of my latest shot at turning this thong into a gaff.