Multiple Select Dropdown Menus

Hi Everyone,
I have a question regarding accessible dropdown menus.  
 
We have list box in which the user can select multiple options.
 
However, when using just the keyboard, it seems the user can only select
options that are grouped together.  
 
For example:
 
<select multiple size="5" id="test" name="test">
<option value="" selected></option>
<option value="1">BSD, Business Systems Development</option>
<option value="2">BSMO, Business Systems Modernization Office</option>
<option value="3">Comp Sourcing, Competitive Sourcing</option>
</select>
 
The user can select option 1 and option 2 by holding SHIFT and the down
arrow... But what if the user wanted to select 1 and 3 with the
keyboard?  

Any suggestions?

Thanks
Scott