I saw this post when you first put it up and as I didn't understand it so I left it for a wiser man. I guess I wasn't the only that couldn't figure out what you need.
You said give id's to the options. Are you talking something like so
<select name="myselect">
<option id="option1" value="index.php?id=1">index.php?id=1
<option id="option2" value="index.php?id=2">index.php?id=2
<option id="option3" value="index.php?id=3">index.php?id=3
<select>
Not sure that there would be a purpose to doing it that way so I am guessing you are asking something else.
But then there is that dummy link which makes me think that you currently have
<option value="http://site.com/directory/option/">http://site.com/directory/option/
in the place of doing it like so
<option value="index.php?id=1">index.php?id=1
I which case it wasn't an id that your are looking for. Of course you could be asking how to set a variable to each option. But that isn't even clear.
We are going to need a bit more information. Maybe even a snippet of your code may help some.