All you should have to do is wire up one PSU to the XE so that when you turn that PSU on (paperclip in the correct pins on the ATX plug and then you can make a proper switch once you have got it all sorted) the vapochill gets down to temp and then just boot the system normally yourself from the button on the front once the vapochill gets cold enough.
Worst that could happen is if you forget to turn the vapochill on, but then the system would just shut itself down once the CPU gets too hot.
Dual rail PSUs dont work well with the 12V Vapochill CC's, the 2 PSU route is the best for ease of use and compatability.
Finding a place for the second PSU can be a pain, some have been put on the floor of the case, others at the rear of the compressor cabinet. Alternatively you can buy a 12V TEC PSU which can fit into a drive bay. You can also get SFF PSUs which are strong enough and nice and small.
The XE draws a maximum of 8.8A on the 12V rail, so make sure you get a PSU with at least 12A on the 12V rail, probably about 14A to be safe.
Hope this helps.
G