You could pass location object variables into Flash at runtime by writing the HTML that embeds the Flash object dynamically with javascript and then appending a parameter string to the movie name. This is from a site I built recently that used that principle:
<script language="JavaScript1.1">
<!--
var strParams = location.search;
var flName = "load.swf"
var flColor = "#000000"
var flWidth = "730"
var flHeight = "425"
document.write('<object'
+ ' classid=clsid

27CDB6E-AE6D-11cf-96B8-444553540000"'
+ ' codebase="
+ ' id="flash"'
+ ' width=' + flWidth
+ ' height=' + flHeight + '>'
+ ' <param name="movie" value="' + flName + strParams + '">'
+ ' <param name="quality" value="high">'
+ ' <param name=bgcolor value=' + flColor + '>'
+ ' <embed src="'+ flName + strParams + '"'
+ ' name="flash"'
+ ' quality=high bgcolor=' + flColor
+ ' width=' + flWidth
+ ' height=' + flHeight
+ ' type="application/x-shockwave-flash"'
+ ' pluginspage="
+ ' </embed></object>'
)
// -->
</script>