associate a hidden input to (chosen) select option in form?

<form action=""; method="get">
<input name="yyyyyy" value="1" type="hidden">
<input name="query" size="50" value="">
<select name="zzzzzz">
<option value="888">YOU-WANT-THIS</option>
<option value="899" selected="selected">OR-KEEP-THIS</option>
<option value="999">OR-CHOOSE-THIS</option>

i'd like
to convert input name="yyyyyy" to a select name="yyyyyyy" (or whatever that can have
more than one value assigned) that is
1 also chosen when user chooses the select name="zzzzzz" option.
2 still hidden (this isn't terribly important, though)

so this
<input name="yyyyyy" value="1" type="hidden">

would instead look something like
<select name="yyyyyy">
<option value="1">1 but you can't see this</option>
<option value="2">2 but you can't see this</option>
<option value="3">3 but you can't see this</option>

except it would actually look like whatever would work :-)

unless this is impossible? or possible only with script?

googling the likes of
associated multiple two-options
gave optgroup or less likely answers