SAN support in PKCS10 request files from certreq

Hi,
 
I'm trying to create a certificate request file using certreq that includes a Subject Alternative Name (SAN), but when I specify the SAN and the Request Type of PKCS10 the request file is created but the SAN is not included in the request file.  If I change the Request Type to CMC the SAN is included, however, our external CA doesn't support CMC format request files.

The OCS Certificate wizard is able to produce request files in PKCS10 format with the SAN included, so it must be possible, assuming the wizard is using the same API set as certreq.

Is the SAN only supported in CMC format request files or is there an additional option you have to add to get SAN included in PKCS10 format requests?

Thanks,
Gary.