Try it out and then let us know.
Actually, please don't. Not that I think it won't work, just that I'd hate to see you ruin your water pump with something that's as corrosive as vinegar. It's difficult to get every last drop of tap water/Restore out of your system (just did it last night) but it's a necessary evil. Whether you do it right and use Restore Plus/VC-9+Restore, the most expensive part of the whole thing will still be the 3.5 gallons of concentrate you'll need to buy so if saving a buck is what you're going after, I'd probably look elsewhere. My $.02