From what I can tell, the integration is bi-directional, so you should be able to do this:
1) Create three GTW events and map to Programs.
2) When lead registers for GTW event 1, a smart campaign adds them to both Programs 2 and 3 as Registered
3) If this syncs both ways, they would receive emails from GTW for reminders. Alternatively, disable the GTW reminder emails and produce these in Marketo
Note I haven't tested this.