Is it possible to submit a form inside an iframe without affecting the browser\'s history?
I\'ve implemented sending a cross domain POST request. It uses Javascript
Does it work to use JS to add an IFRAME whose src is hosted at your site (the domain to which the third-party-hosted script needs to send data?) This IFRAME could include the needed Javascript to make an XMLHttpRequest to your/its domain. And as for getting the actual data to this IFRAME from the third-party-site - try: http://softwareas.com/cross-domain-communication-with-iframes . It's a pretty clever solution involving changing fragment identifiers (#something) at the end of the IFRAME URL, which you can then read via JS within the IFRAME.
Also a guess, but if you tack this past SO solution to a similar history problem (using location.replace) on to the above this hopefully should let you do the anchor-changing part without disrupting the history stack.