Yes, you can invite a lead partner to co-brand a lead.
1. Select the Leads panel from your dashboard
2. Select the lead you wish to invite a partner to co-brand
You will be redirected to your leads information (See Image)
Here you will see a box for Lead Partner( the second box on the left of this page)
3. Click the Co-Brand Lead button
The Co-Brand Lead Box will pop up 
4. You can search contacts to add an existing contacting or manually enter in the name, email address and phone number of your Lead Partner
Note- Lead partners have access only to contact information and maintain their own communications log.