I think a belt sander would work best so you can have contact along the entire length. A fine grit, light touch, as you roll it gently.
My second choice would be to clamp it in a vise and use a random orbit sander to run up and down the length... with fire grit you should be able to control the rounding easily.
I assume you will only round the bottom edges and they shouldn't need to be fully rounded like the short point of a skew. Each bottom edge rounded about the diameter of a pencil lead will be round enough to not dig into the rest. If it is not enough for you re-do and take just a little more off.
I agree it would be difficult on a 3/4 -1" grinder sliding it across and rotating and getting a smooth edge over the length.
I have rounded all of mine slightly.
They who can give up essential liberty to obtain a little temporary safety, deserve neither liberty nor safety. Benjamin Franklin