Hi Jeff - I haven't heard of anyone being able to do this successfully with the Marketo connector provided by Sugar.
This was actually point #5 in this article I published just this week.
Bedrock Data offers a reasonably priced third party connector to get opportunity data back to Marketo from Sugar, and power up Marketo RCA.
Thank you for passing over that information. Sugar's own documentation on the Marketo connector actually highlights how opportunity information gets synced over to Marketo, so I know this functionality comes natively. What I'm struggling with is how.
Either way, I'll keep working on this and I'll explore 3rd party solutions if it gets to that point - hopefully not!
Super Jeff, sounds good.