Is there a command in Vim/gVim to combine two or more tabs into a single split window?

Is it possible to take two files that are open in separate tabs in gVim and combine them into one tab with a split/vsplit window? I'd prefer if there was a way to specify which tabs to join, but even something that is the opposite of :tab ball would be good enough.

Thanks

There are a couple of functions published on the “Move current window between tabs” page in Vim Tips Wiki that should do what you want, or be easily modifiable to get exactly what you want.