[exim] different quota sizes for different users?

Is there some way to configure quota differently for different mail
accounts???

In the configure file there seems to be only one set of quota settings
in the local_delivery section. It would be very useful if there could be
more than one tier, so that some high volume users could have larger
quotas. For instance, one account is a destination for PDF files and
tends to fill the 20MB quota in a hurry, whereas other accounts would be
fine with even a 10MB quota.

Thanks,

David Mathog
mathog@???
Manager, Sequence Analysis Facility, Biology Division, Caltech