Did you find any solutions on this one?
Im also looking at this. I have found this page: http://social.msdn.microsoft.com/Forums/sl-SI/sharepoint2010general/thread/0753df63-8b30-4594-a8bd-ef8ba9514103
They list supported and unsupported column types. Choice should be supported, but it is the Choice columns that isn't working for me.
/David
You could create dummy fields (Single Line of Text) to be populated in a SharePoint Designer workflow with the option "Set Field as Value" for all new items (or also changes in all items) that sets the dummy field to the selected choice field. That dummy field will then appear as available to select and link.
A solution that I found was to add a calculated column on the look up list to return a single line of text entry based on the value that I was looking for its not very elegant, but it did the trick