The DistributedVirtualSwitchHostMemberPnicSpec object allows for the attributes

UplinkPortgroupKey
UplinkPortKey

So you should be able to select the UplinkPortgroup perhaps even the specific port within that group, if it makes sense to do that. However I have not tried this but will update my lab and give it a shot and comment with my results.

The object reference is located here, http://www.vmware.com/support/developer/vc-sdk/visdk400pubs/ReferenceGuide/vim.dvs.HostMember.PnicSpec.html

I would recommend reading all of lucd's blogs, http://www.lucd.info/ there is in depth information in them on networking and adpaters as well as other things.

Regards,
John