Prior to answering your question, I wish to clarify that the approach which you are intending to take to trigger an event on bounced users isn't a good option; as you could filter down on such sessions in your analysis later but you cannot get back the lost data. Regarding the use of a single profile on multiple websites I strongly discourage this as well since it would complicate tagging across your marketing needs. The benefit would be that you only to update a given change once, but managing them for 30 distnct sites would complicate tasks a lot. Nevertheless, if you wish to proceed with the above, you could do so by using a JavaScript extension and writing a bit of code to trigger when the user is closing the tab or browser. Thereafter you could use location.hostname to check for the particular website which you want to trigger the event on. You may need to manually code the event such as, ga('send', 'event', [eventCategory], [eventAction], [eventLabel], [eventValue], [fieldsObject]); As if you could the utag view or link calls it would cause other issues if you have other events in place on the same page.
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