A can instead of a cone might work, but I doubt it would be as efficient. Stoves like the Ledmark etc. are pretty well tuned to get the airflow right. You want cool, oxygen rich air entering from the bottom, flowing up past the burner and then up the sides of the pot in a controlled fashion that doesn't allow any outside gusts to rob you of heat.

The burner itself needs to be of a proper design so as to get the air/fuel mix right. Sterno cans are hardly the ideal stove. They're pretty lean on the air. Sterno is designed for long slow heat and really isn't all that good for cooking, more for keeping something warm.

When the Ledmark is only $20.00 I guess I'd probably just go for the Ledmark which comes pretty well recommended by the guys I've talked to who have one. Of course if you're into DIY, you could try a can stove and see if it works well.

HJ