The marketing suspend method sounds pretty workable. If you didn't want to work off some extra field though, you could simply watch for leads created from source=CRM or prospecting or whatever you use, and only open up email when the lead status goes to cold, or some other status that tells marketing it's time to engage.
We actually find more and more that once the leads are in our sales teams' hands, we are enabling them with published, marketing-approved templates more than we are messaging on their behalf. It takes some trust between Sales and Marketing to ensure leads aren't being left behind or neglected (and conversely that Marketing's messaging is good), but it's a very efficient and productive dynamic to reach for both sides of the table.