Notes/Domino 6 and 7 Forum : Migrating from Exchange5.5 to Domino R6

Hi
I am migrating users from Exchange 5.5 to domino R 6.01. The mails from the Exchange mail boxes are downloaded in the Personal Folder in the PST format on the local hard disk of the user.After the users are migrated we are migrating the PST which are at the local hard disk of the users.We are using nupgrade 3 utility to convert the PST to notes mail file.The PST is getting converted properly, but there is one issue i.e the mails which are in the sent items of the personal folder, In the who column the display name is coming of the migrated user instead of the person to whom the mail is being sent.I have to change this names to the recipient names to whom the mails are being sent.
There is one way that I open the mail file in the designer & select the sent item folder & for the who column instead of "Formula" which is there right now I select "Field" & sent to & save it then the display name comes proper.
But this I cannot do as there are 400 users & individually cannot be done.I need to create a template which will reside on the server & then I will replace the design of the mail file with this template so that only "Sent Items" folder design is replaced.Can any one suggest me any solution for the same.
Thanks in advance.