Hmm... a possible (untested) solution would be:
1) Create separate tokens for everyone with an custom attribute containing the "collaborative" token that they should access.
2) Modify the invitation email template to include a custom survey URL appended with the token attribute value.
Of course, that would render the reminders function useless but I don't see how that would work with multi-collaborators anyway.
You will also need to figure out a way to ensure that the collaborators don't access the survey concurrently, overwriting each other.
1) Create separate tokens for everyone with an custom attribute containing the "collaborative" token that they should access.
2) Modify the invitation email template to include a custom survey URL appended with the token attribute value.
Of course, that would render the reminders function useless but I don't see how that would work with multi-collaborators anyway.
You will also need to figure out a way to ensure that the collaborators don't access the survey concurrently, overwriting each other.