where to define sendto function?

On my site, the IMCE window opens using the following url:

http://mydomain.local/imce?app=tinymce%7Csendto%40myIMCESendTo

This was achieved by tweaking the IMCE Bridge module. I have also defined a function myIMCESendTo in the IMCE Bridge javascript file myimce_wysiwyg.js. This is the same file as used by the IMCE Bridge module where the IMCE window is open using win.open (only I changed the name).

However, it looks like IMCE does not find myIMCESendTo() function. Also in the browser debug window (I use Chrome) when checking the new IMCE window loaded scripts, there is no javascript file myimce_wysiwyg.js loaded at all (it is loaded in the parent window only)

More precisely, there is line 42 in imce_set_app.js checking for sendto function:
if (appFields.sendto && (func = isFunc(appFields.sendto)))
and isFunc(myIMCESendTo) returns false.

By the way, for testing purpose, myIMCESendTo is defined like this:
function myIMCESendTo (file, win) {
alert ("aa");
}

and no alert is displayed when a file is chosen in IMCE. That's another proof that this function is not found.

So, where to define this sendto function?