using helpers outside the systems folder

[eluser]Philipp Datz[/eluser]
hello, maybe an easy question, but i didn't find a way to handle it, neither in the userguide nor in the forums.
the structure of my application looks like this:

application
assets
system

application outside the system.
assets for js/img/etc.
and system.

im storing my js files, in that case mootools-functions and stuff in assets/js, but want to use the uri-helper for the url in the ajax requests. is there a proper way to include/load the helpers in that place?