Paneling and Trim - Baseboard trim on curved wall

I need to install baseboard trim on a curved wall. It will require a 7ft length. The curve forms about a half circle. The rest of the house is being outfitted with MDF 4-1/2 inch wide and 9/16thick. My questions:
Has anyone ever tried to work MDF into such a curve?
How would you go about doing it? Would cutting small kerfs in the back of the base work?
Should I use wood and try to find a matching profile and then cut kerfs in the back?
Should I use the various "flexible" trim products I see on the web?--I did find one (trimster.com) that has a base with the exact profile and size. ( I think they made that base to mirror the product I'm using). --It's awfully expensive --about $60 for the 7 ft piece.
Can anyone recommend a flexible trim company?
Any recommendations would be welcome!

You can't moisten MDF, as it will break down, so trying to form it is out. If you can find the profile in solid wood (not finger jointed), you can form it. It takes a long time, but making a movable jig that will close the ends gradually, spraying it with water daily, you can achieve the bend you want.
I have had to bend wood, not the way you are, but in the opposite plane to replace one missing from a factory rounded door frame. Took about a week to form the wood.
You may be able to find flexible molding by googling it.