I found this useful h**p://wxw.reteam.org/papers/e42.pdf

quick fix with orca
 

The image below shows the minimal changes in msi tables needed to
bypass the serial.
You will notice that the custom setup dialog is displayed twice.
This can be corrected, but some more table editing is required and I'd rather
not devote the time as the main thing is accomplished.

A little explaining:
This setup was a little more clever in that the Next button had a DoAction of
resubmitting itself [CustomerInformation_Next] until a valid serial.
But .msi is always the weak link as you can change the action to display another
dialog (in this case CustomSetup) further down the installation sequence.

Look at the picture with "before"->"after" comparison and you'll understand what
I mean.
Regards.