Adding Links to Document Library that share columns with documents in SharePoint

Hi:

I'm trying to add the ability to add links to a document library in SharePoint Foundation.  As one of the properties, of the document library I have added a column called Sector which is a dropdown with 4 items which one can select with check boxes, say fruit, vegetable, meant, grain.  

I'd like to add links to external web sites that are of one of these types so that whe the user filters on say fruit, only documents and links of sector fruit are visible.

I've been able to add the Link to Document as one of the content types in my library and am able to add links.  However, the custom  sector column that I added for documents is not available for link types so I am not able to filter links according to sector.  

Any help in enabling me to filter documents and links in the same library according to one common field would be greatly appreciated.

RBS