What started out as a variation on a Sacher Torte has turned into a roulade (mostly to justify my recent purchase of a jelly roll pan). I think I've got it figured out exactly how I want to do it, except for one thing. I want to coat the whole thing in ganache, kind of like a giant Ho-ho. I'm going to be using pretty expensive chocolate, so I want to waste as little as possible. How can I evenly coat a cylinder with ganache? I'm going to roll the whole thing in chopped hazelnuts, so minor imperfections won't matter.
You'll definitely want to freeze the cake. Once it's frozen, use a spatula to apply a layer of ganache to the side that will be the bottom of the cake, then return it to the freezer. Once that has set, put the cake, ganache/bottom down on a cooling rack on top of a sheet of parchment paper or acetate. Slowly pour your melted ganache over the cake, guiding it with a spatula if necessary to make sure you get it all covered. You'll want the ganache to be just beginning to cool for a thicker coat. Once it's coated, you can roll it in nuts or whatever you like. You'll have a grid pattern on the bottom (depending on how solid the first ganache froze), and possibly some "feet", but the feet are going to be almost unavoidable.
Any extra ganache will be on the parchment or acetate and can easily be stored until you need it again.
Hohos get that perfectly smooth coating all over because they are dipped. And it is far from real chocolate; it is a formulation engineered for the purpose.
This would be better done with tempered coverture (which would obviously best show off the quality of the chocolate) or a sugar based chocolate glaze, rather than ganache (although a stiff ganache might work, but would require some experimentation). It wouldn't taste good, but this is one case where sadly commercial "chocolate" coating will perform well, at least in adherence and smoothness.
You would need to make your rolls small enough and sturdy enough to facilitate dipping. Chilling them in the fridge for an hour or so couldn't hurt; experimentation might even indicate that the freezer works better.
Dipping is also not in line with wasting as little as possible; in fact you need a considerable surplus. It normally is reusable, and finally put into other things as an ingredient, but you do need it for the dipping operation.
You will need appropriately sized dipping forks, or an improvised rig (such as a fish spatula bent to 90 degrees) with which to dip the rolls, and a sufficient volume of glaze to allow them to be immersed briefly.
You may require two dips to get a good application.
If you really aren't worried about the appearance, I would simply ice them with ganache using the traditional icing spatula, and roll them in the nuts. Who will know what was smooth or not smooth?
I can understand why you'd like to do this, however I would steer you clear of it. A roulade is very light, and if you coated it with a ganache you'd overpower it completely. Try drizzling a cherry, mint, or chocolate sauce over a slice in a fancy way instead, it will look and taste amazing.