I just committed something to Git master that I hope is able to fulfill your needs:
Test profiles can now call $SYSTEM_MONITOR_START and $SYSTEM_MONITOR_STOP. Below is a brief example of one I hacked together to demonstrate for an install script for a test profile:
What that does is monitor the memory usage every 1 second while launching Firefox for 10 seconds. The memory usage delta/difference is then determined.
\$SYSTEM_MONITOR_START mem.usage delta 1
firefox http://www.phoronix-test-suite.com/ &
\$TIMED_KILL firefox 10
\$SYSTEM_MONITOR_STOP > \$LOG_FILE" > idle
chmod +x idle
$SYSTEM_MONITOR_START has three parameters. The first is what to monitor (currently what's implemented right now is mem.usage or cpu.usage). The second argument is for average, maximum, minimum, delta, or all. The last argument is the amount of time (in seconds) between polling results.
Running $SYSTEM_MONITOR_STOP then stops the polling and will return the value.
Let me know how that works out for your needs or if you hit any problems or need any other features Patches are also welcome along with new test profiles.