Yep.
In LD, 15, you can adjust the intercept treatments of any type of call. I believe the entry for non-defined DID's is CTVN (Call to Vacant Number), and if you set the options to OVF OVF OVF OVF, any call to those numbers will be given busy or overflow tone. You can also set it to BSY, but I think it is the same to an external caller.
Hope this helps,
Scott M.