Newbie fillet edge when surface is not wide enough

Hi,

I want to fillet an edge on an object created through lofting and boolean operations. The fillet should easily be possible but I encounter a problem. When I explode my object it turns out that the bottom surface is in fact two surfaces and the one connecting to the edge I want to fillet is not wide enough to allow for the size of the fillet I want. I've attached the offending parts in a rhino file.
I've tried to join the two parts of the bottom surface but that (obviously) does not help.
What's the, most likely very simple, solution to this problem?

Thanks,

Arjen

Attached Files

• Fillet.zip‎ (82.2 KB)