Auto importing, for now, has no way of differentiating between travelers and will import all confirmation emails in your in-box.
The best work around we can offer is to turn off the functionality in your account that automatically places imported plans into trips. When this occurs, all new plans are placed in your unfiled items file (http://help.tripit.com/entries/205382) and you will be able to move the plans into an existing trip, create a new trip for the item, delete the plans, or leave them in your unfiled items file.
To turn off the auto placement of plans, after logging-in, click on your user id (upper right of any page), select Settings and then select About you in the left nav bar. On the About you page scroll to the very bottom and in the category Unfiled items uncheck Put new plans into trips. Be sure to select Save before exiting the page.