Paul
You can do this on a layer by layer basis...
If you set up your cue with DMX - then turn off the DMX control of that layer in the catalyst control window - the values will remain until changed.
This means that you CAN scrub to the correct point manually
Once done - switch on the DMX controller on the Catalyst Control window to re-gain DMX control.
You can also enable / disable DMX control via the 'control/ tab on the webserer.
Simon