[Chameleon] Filter selection for QuickZoom

[scdyoung at tpg.com.au]

To whom it may concern, 
 
I have identified a requirement to perform a quickzoom from a 'dynamically' created select list - such that 
the first of 2 select lists provides a list of reference layers (simple enough), and the second (which is 
where it gets tricky) provides a list of regions (and extents for each) contained only within the selected 
reference layer.  Note all extent information is stored in a Postgres database. 
 
I am currently able to create a 'quickzoom' tool via generating the <select></select> content in my 
index.phtml from a database call and outputting it all in my template through the use of [$|$] 
pre-processing (thanks Jason! ).  The issue is that I need to set whats gets pre-processed in the template 
dynamically (from another select drop down) and I'm not sure how.   I would be most grateful for some 
direction. 
 
Note that I can get it all working with javscript and pre-set vars(extents), though it makes the client end too 
heavy - especially given that the list of reference layers is expected to grow considerably. 
 
Regards 
 
Dale