The CPU load is the percentage of time the CPU wasn't in the idle loop. The command Trace.PROfileChart.TASK gives such a percentage view. You just have to identify the "idle" task(s). Please note that an OS awareness has to be loaded.
1. Create a task group for this task with merge or hide option:
GROUP.CreateTASK "idle" "<my_idle_task>" /MERGE
GROUP.CreateTASK "idle" "NO_TASK" /MERGE
2. If the chart should not distinguish between the other tasks, you may also merge them:
GROUP.COLOR "other" MAROON