Cross-domain user tracking and Sub-domain site scenario How To?

for our scenario, we have our sub-domain we will call Classifieds set up with your plugin as a stand-alone Google Analytics tracking code account.
Is it possible to use Cross-domain user tracking, somehow to track the same domain to our parent site also?
We would like the parent site recording the overall traffic of the sub-domain, to show total traffic to both sites, is the main reason.

Any suggestions on how to accomplish this in Google Analytics, with help from this plugin?

If not, also possibly some other scenarios of when you would use Cross-domain user tracking.

Thanks,
-crssp