Recording to an external firewire HDD in Pro-res via Intensity Extreme & Media Express

We are going to be needing to delay our usual live stream for approximately 30 mins.

Our normal workflow is:

6 Camera's into BMD TVS and HDMI program out into Imac & Wirecast via Thunderbolt Extreme. Audio is fed directly from mixer into component audio on Extreme.

In this workflow there is no provision for a long delay. We were hoping to be able to record the video via media express in 30 minute chunks and then play the files in wirecast but once wirecast is open it hogs the Extreme and media express cannot access it.

Our thoughts then turned to recording the video on a macbook pro using Pro-res LT codec via extreme/media express onto firewire hard drives which we can swap out every 30 minutes to use the clips on our streaming Imac.

Has anybody tried anything similar? Can most firewire drives support this? Any drawbacks or flaws that we are missing?

The last time we needed to do this we were working with analog and the BMD USB TV recorder did the trick for us.

Thanks in advance for any help!