[Exim] message_size_limit

Is there a way to setup per-user message_size_limit in transport?? And
how do you achieve this? I've already found out
that doing something like this:

message_size_limit =
${lookup{$local_part}lsearch*{/usr/local/exim/msgsizlmit}{$value}{2M}}

does not work because message_size_limit expects a literal number.

Is there a better way to go about this, and how?

Thanks in advance,
jAmIe

~ Jamie P Bontrager ~
~ Network Assistant ~
~ KCTC.net ~~~~~~~~~~