[TxMt] Compound regular expressions in snippets

I'm having a bit of trouble trying to work out if it's possible to have compound regular expressions in a snippet.

Basically, I want to replace all spaces in a tab-stop with hyphens, whilst also lowercasing the whole string -- two things I can happily do separately:

${1/.*/\L$0/} ${1/ /-/\g}

but can't seem to work out if it's possible to do both at the same time. I've tried replacing the tab-stop in one expression with the output from another:

${${1/ /-/\g}/.*/\L$0/}

but it doesn't work. I know it's possible if I create an intermediate tab-stop like this:

${2:${1/.*/\L$0/}} ${2/ /-/\g}

but I don't want to do this as I have no use for the intermediate value.

Any help would be greatly appreciated! Thanks in advance.

Jordan