i don't think it's wsusutil deciding on the temp location, that's a global windows environmental path variable which you would need to change and it would apply for everything that requires scratch space under temp. worth it if you're that low on space,
so you can at least get your exports done
look for variables named TEMP and TMP and redirect their paths to another disk - this will create complications with some applications so be careful and take note of their existing paths so you can revert the change if required
I've never looked inside the cab file but I think it does everything, but it's still fairly small in size