If you kill the yeast, you can't carbonate from what I've read, which is the main reason you would need to use a non-fermantable sugar. So you can sweeten and then add carbonation.
This is reference to party kegs of beer like bud light/Natty Light/etc... Pouring just 3 or 4 glasses worth of beer without pushing an alternate source of CO2 will not have any noticable affect. And then you adjust to the desirable pressure. When I speak in reference to slowly raising pressure...
I would take their advice on finding/fixing the leak.
I have had this configuration on my home Kegerator and the method I found best for getting the LEAST amount of foam was to do this:
DON'T Turn on the CO2 tank until...
AFTER You tap the keg...AND you fill up a few glasses or a pitcher of...