Sue
Do you use a different profile to work days to weekends? (profiles = programed basal rates)
I wonder whether that your problem lay within the driving part of your mroning? As driving in peak traffic can be stressfull with out us really realising it, this would increase your BG's...
Another part concerning the driving, sounds daft I know, but where is your infusion set and pump located, as for the infusion set, this might actually be having presure of clothing, seat belt, or even the body that is restricting the flow and/or the asorbtion of your insulin, enough to effect your BG's but not enough to cause your pump to alarm a occlusion warning?
What I would do, is take a BG before heading off to work, then when I park at work, note down what sort of drive it had been, cold icey, lot of traffic, loads of bad drivers, delays rtc.then follow with 1/2 hours testing, over several days to see if any patterns build up with relation to the journey.
As it could be that your basal is out and needs tweeking to cover better, it might be that you can't set a basal rate for this period as such, but if you can work out what factors send your levels up or down, then you can use a temperory basal rate, to over come as required.