been quite busy in the last days but had some progresses anyway in the imagemap side:
the quick'n'dirty solution (with a modified version of the buildQueryString function) is properly working, updating the map at every click. So cool stuff!
Probably not worth committing the whole js stuff for sending imagemap.x and imagemap.y request-params (as it's based on the 2.1.9 ajax support) but maybe only the ImageMap.java widget support for BrowserUpdate (via autoadding to form.updatedWidgets).
PS. Are you sure this will look good though ? If what you are doing
is just re-centering the map on the new coords, I'd be tempted to
write a Dojo WIdget to handle this itself, give you a smooth scroll
to the new centre (everyone is used to Google Maps etc.) rather than
replace the image using BrowserUpdate. (Just my humble opinion ;))