Can we just use sugar as our prime fermentable, and add other stuff in the secondary?

Some folks take an approach like this for making cordials. Use sugar to make a high gravity batch - perhaps even a Turbo yeast to get over 20% ABV, then charcoal filter to remove off flavors and then add whatever fruits or flavors are desired.

I supposed you could make a sugar wine and then add flavors to it in the secondary. I don't know how good it would be, but if you try it, please keep a brewlog on it so we can learn with you.

Medsen

A lot of fruit wines use sugar to boost the alcohol content to "normal" wine levels. I know there are several recipes floating around using a few pounds of fruit and 10-20 lbs of cane sugar. They sound like they often produce some hot flavors that last a considerable length of time, so charcoal filtering or just plain waiting would be good.

A little less extreme would be to supplement your meads with some cane/corn/beet sugar to lower the cost but not significantly alter the flavor. Belgian beers, for example, usually use some simple sugar to boost the gravity; this dries the beer out as well but you don't get the "fermented cane" flavor. Try cutting the honey with about 25% cheap sugar.

I haven't tried it myself, so I'm just going off secondhand descriptions. I'm guessing it's not that cane sugar causes "hotness", but that it doesn't cover it up as well as other sugars (honey, barley, grapes) which have flavors. Basically you turn sugar water into alcohol water with almost no other components, and you're going to just taste the alcohol and other fermentation byproducts. The more "other stuff" you add, the less you will notice the "hot" flavors. Conversely, the more cane/corn/beet sugar you add to your beer, mead, or wine the more hot flavors you will notice.