One solution is to only sample the pages/users of interest; selecting the sample could occur on the server and/or client. But another solution would be to collect statistics across multiple pages and periodically send batches of analytics to the beacon URL.
I've been playing with mobile web development for agilitycourses.com lately and will soon let users store the courses they create in localStorage on their browser. That got me thinking that sessionStorage could be used to store analytics across pages and then periodically send the stats to the server. This would reduce the number of hits on the beacon, allowing deployment to a larger sample of clients. It also gets flushed once the session is closed and (if kept small) doesn't prompt the user to approve storing the data.
A lot of modern browsers support session storage and for my purposes only ones with support would be relevant - due to our browser support policy at work.
The other problem the boomerang docs discuss isabuse of the beacon (accidental or malicious). A solution would be to piggyback reporting of analytics into application form post payloads. This is trickier to implement and it suffers from coupling analytic reporting into the application itself.
To try to solve it some what generally... The client side JS library could add a hidden field to any/some/specific forms into which it writes the analytics data collected thus far. If it hooked the form submit callback it could know if the form was successfully submitted and clear the session storage.
Server side middleware could detect the hidden analytics field in the form and extract/store the data. It could also remove the field before passing the request data along to the app server.
All in all a fair amount of twiddling to keep from exposing a recording URL to the outside world.
Of course if an authenticated session was being used then abusers would have to have a valid session to post to the beacon URL.
I don't know if I will have time to play with the sessionStorage idea but I think it might be a worthwhile extension to boomerang or other client side analytics capture libraries.