I use a couple of workarounds.
For small forms I use the function that returns the entire form as
query string.
For larger forms I like to include both files in one so that no
redirection is needed (vt_include is an include function I
wrote):
if {some_condition} {
set page page2
}
switch $page {
page1 { vt_include page1.tcl }
page2 { vt_include page2.tcl }
}