Jon,
This works in ad_form for me:
set all_widgets {}
lappend all_widgets \
[list start_date:date {value {[util::date acquire clock [clock scan 2003-01-15]]}} optional]
ad_form -name spell \
-mode edit \
-cancel_url / \
-cancel_label "Get outta here" \
-confirm_template confirm \
-spellcheck_template spellcheck \
-spellcheck_label "Spell Away" \
-form $all_widgets \
-on_submit {
# What now?
}