You can definitely add your own channel to a Bitly campaign! When creating a campaign you have the option to select an already existing channel or create a new one. You can have up to 100 channels per campaign.
Within the Edit Campaign section select Manage Channels.
From here type in the channel you would like to add and select Create '[new channel]'. For example, type "Paid Twitter" and select Create 'Paid Twitter'.
The channel will be added to your list of channels automatically. From the Manage Channels section select the arrow to return to the edit section.
Now from the Edit Campaign section search for your newly added channel and select it.
NOTE: Each Bitly account can have a max of 500 individual channels