Using the ideation portal for aha is nice, but there needs to be a way to have a conversation with select people about the idea. It should be attached to the idea so that it can be tracked. Right now, the only conversation is via the forum where it's either public or to the idea creator... Or using a 3rd party tool...
If you look at the idea in Aha! you will see the "Public comments" and "Private comments" tabs at the bottom of the idea. Private comments are exactly what you are looking for - they are only inside Aha! and are not visible in the portal.