We want to define custom fields that will behave similarly to "Admin response":
Only Aha users can edit them, but portal users can also see them.
This is currently possible. When adding custom ideas fields, there are three options for where those fields should be displayed:
Ideas (inside Aha!)
Fields that are available on the ideas layout and ideas portal layout will be editable inside Aha! but read only in the portal. You can see an example of this in our own ideas portal -- the Release time frame field.
This article explains ideas custom fields in more detail.