I've been playing with DSL Tools and the LINQ preview. Apparently the LINQ preview contains an obsolete version of the DSL redist, used for the DLINQ designer. This means that installing the LINQ preview will break your DSL Tools: the symptom is that text templating fails. The workaround is straightforward; either install LINQ before you install the VS SDK, or reinstall/repair the VS SDK after you install LINQ. This will probably break the preview DLINQ designer, though.
Anyway, once you've got it working, you can write LINQ code that runs against a DSL store:
var elements = from e in model.Elements where e.Name.Length < 5 orderby e.Name ascending select e;
This will help to write constraints!