Thanks all, this works indeed!
There is one more thing, I had to use $parameters. to pass input variables to the new screen via the url, that works as well, but one parameter had to be converted to an url friendly string.
I'm not sure what the exact term is for this, but to illustrate :
"/FileCache_CS/rest/FileStorage/GetFile?Id="
had to be converted to this, to make things work perfectly
"%2FFileCache_CS%2Frest%2FFileStorage%2FGetFile%3FId%3D"
I have done this hard coded in the input string, as you can see below, but surely there must be an action or a function available that handles this properly, anyone knows about that? Bonus points if you can tell me the technical term for this type of conversion. :-)

