Get originating LeadID from Opportunity record when sending email (Processes)

Scenario, my site registers a Lead, it gets created in CRM (SOAP), I get the Lead GUID back from CRM to link the two. When sales qualify a Lead in CRM, the Opportunity is created and Originating Lead field is populated with the Lead GUID. I now want to send an email every time one of these Opportunities are modified but I require the Lead GUID.

In the email template I can place {Lead(Originating Lead (Lead))} but this returns the Originating Leads name not the GUID, is there any way to obtain the actual Originating Lead's GUID in the email templates?

Thanks

Paul.