How to track free events, where registration is required?

How do you track free events, where registration is required (or a liability waiver is filed) but no ticket is issued?

This year we hosted a free yoga series on Fridays  in June, July, and August.

So far about 200 people have participated.

We want to store participation data (for the 2014 series, not individual Friday yoga dates) at the Constituent level.

We want to be able to pull participants via Lists/Extractions based on the years they participate (we are definitely planning to offer summer yoga again next year).

In the constituent record, under Research, we have considered using Note Type in KCYOGA and pulling by Note Created Date ranges...but this seems like it might get messy when we've got more than two years of data to work with.

Any recommendations would be appreciated.

Thanks.

Chris