The question is as asked. My intended use case for this would be to have something like minipage, but whose height can be set using glue, rather than only a dimen.

When the page is pretty easy to split up, I can just use \textheight to divide things, but sometimes there's extra text on the page, and what I really want to instruct TeX to do is just how to use the remaining space on the page, aside from the stuff I've already typed. I figure the way to do this is to put glue in a box, and once the glue's been set, replace the glue with a box of the same dimensions.

The question is as asked. My intended use case for this would be to have something like minipage, but whose height can be set using glue, rather than only a dimen.

When the page is pretty easy to split up, I can just use \textheight to divide things, but sometimes there's extra text on the page, and what I really want to instruct TeX to do is just how to use the remaining space on the page, aside from the stuff I've already typed. I figure the way to do this is to put glue between boxes where content would've gone, and once the glue's been set, replace the glue with a box of the same dimensions.