Todd Klindt posted an unknown STSADM command that you can use to change the max capacity of a site template. The command you need is:
STSADM –o setproperty –pn max-template-document-size –pv 524288000
The –pv value is the value, in Bytes, that you wish to set the limit to. The maximum value that can be set is 500 MB or 524288000 Bytes.
Note: STSADM will crunch away at this command for a while so be patient and PLEASE do NOT terminate STSADM midstream!