If a friend and I wanted to share an account, is there any way to lift the restriction of only having one computer logged in at a time?

There is no way to lift that restriction and sharing an Accelerator account is in violation of the Accelerator Terms of Use. Also, note that the system tracks progress and issues a Certificate of Completion to the individual whose name is on file. So even if it was possible to share access, only one individual would be able to claim completion of the program on a resume, LinkedIn, etc.