Url as controller function parameter

[eluser]enigmas[/eluser]
Guys, please help me out to fix one, I hope that very small problem...

I need to carry to controller's function a parameter which is really - url string. I encode url string by using urlencode firstly.

So my url is looking like:
http://localhost/index.php/login/index/http% 3A% 2F% 2Flocalhost% 2Findex.php% 2Fadmin
(I kept spaces in url to avoid forum formatting...)

When I call this url I aways get a "Not Found" page... looks like codeigniter decodes % 2F anyway to / and thinks it is another parameter... Is there any way to fix it, except using some other way to encode parameter's url?