Is ALM 11 required to install Performance Center 11 Servers?

Although we are licensed for Performance Center, we typically run tests directly form the controller (PC 9.5.1). The PC licensing was primarily to have multiple controllers and share agent licenses. All scripts and scenarios are stored on shared servers (not in PC).

QUESTION: Do I have to install ALM or can I mimic our PC 9.5.1 install and install just the PC Servers?