Can you bump the fixed WB color temperature up and down?

My Z1s are set up to bump the fixed Daylight White Balance up and down using the user buttons 2 & 3, so I can have repeatable consistent white balance in environments where daylight and tungsten mix. For example, 0 is Daylight, but +2 is great for warming up overcast days, and whilst -5 is officially tungsten, -6 is great for stage lighting at half power (so as not to blind the presenter on stage).

It's great. It's not perfect, but really really useful. Can the EX1 do this?

No the EX1 can't do this as conveniently. What it will do works just as well, if not better. You can access the WB through the Picture Profile menu. Here you can dial in whatever value you want and even set an offset for your "A" or "B" white balances. This is good because I've noticed that setting your white balance with this camera isn't as consistent as the other Sony cameras I've owned. (DXC 30, VX 1000, Z1).
-Tony