I don't think there is anction for that porpouse, however you can put the variable in a table and make the user click the XL export button. The dim and expression might look something like this:
Dim -> valuelist('v1','v2','v3')
Expr -> pick( match( valuelist( 'v1','v2','v3' ) , 'v1','v2','v3' ) , '$(v1)' , '$(v2)', '$(v3)')
There is an action to export to a file. Works fine. I can even export multiple objects with the append option.
I want to export a "variable" retrieved from a user input. I even tried to spoof this by adding a bogus field and assigning a variable to it. Then writing; that field to the file. It does not seem to work.