Set root domain for sites with multiple domains

We (Coccinella project) have 2 domains that link to the same website. Both domains are equal in importance (some kind of a backup). The issue is that the Diggthis plugin can't handle this correctly. If a story gets submitted using the one domain, the diggs are not visible when people view the digged story using the other domain.

An example:
http://coccinella.im/whytransportsmatter <--12 diggs
http://thecoccinella.org/whytransportsmatter <-- 0 diggs

A reverse example:
http://thecoccinella.org/eat-a-bug <-- 3 diggs
http://coccinella.im/eat-a-bug <-- 0 diggs

The solution may be that I can set a default domain in the Diggthis settings that will be used for all stories, whatever domain is used to publish the story to digg.com. This domain then also is used to get the number of diggs, whatever domain is used.