Simple enough. Convert the object in question to curves, if it isn't already. Then...
Activate the 'Select Point' tool.
Marquee select all of the nodes on the object.
Activate the 'Round Corner' tool. A shitload of little circles will appear on the object.
Set the desired radius in the Design Central dialog and apply. Only corners that can be rounded to this radius will be affected. All other nodes will be left unchanged.
Or you can take the cowardly way out and merely add a small stroke with rounded corners. Separate the stroke and weld it to the original object. This makes the object a tiny bit fatter but it preserves the nature of the object, like text. You can always clear the weld and delete the object that was the stroke.