Excuse my really bad uplevel hacking, but the following does the trick:
replace
set value [uplevel subst \{[lindex $var_spec 1]\}]
with:
set value [uplevel set fasldkjflaskd \{[lindex $var_spec 1]\}]
if {[info exists form_var_list] && [lsearch [lindex $var_spec 1] $form_var_list]> 0} {
# don't run subst on auto included form vars
set value [subst {$value}]
}