Thanks for the info, Jeff.
I wonder if setting up automated RingLead de-duping in Marketo, as I've done, would help you out.
What I did was implement the manual method they
outline here (be sure to see my note re: trigger vs. filter). Next, I added a new Smart Campaign in the same program ("01 Ongoing: Add Dupes to RingLead Dedupe List"), which runs nightly and checks for Duplicate Fields: Email Address, then adds user to the RingLead Dedupe List, which triggers the RingLead webhook in the other Smart Campaign.
Here's the automated Smart Campaign I have setup:



