Modify URL before sent ajax request

Hi,
i have a problem with ajax URL, i need to change and append "/" before the reale URL.
Below the example ajax request:

$get("mypage.php"......

i need to append "/" before mypage.php, and so modify the ajax url request.
I tried with ajaxSetup beforesend without success...

Thanks

ps don't response $get("/mypage.php"....