During my boredom ...

[pd]

A band brake might also work.  I've seen them on old mini-bikes.

I wonder just effective that would be . I would think application would be very easy and might not be nearly as noticeable when completed .

Pete .

[Eitek1]

For some reason I didn't catch the roller when I first looked at it. Assuming you could supply enough force (which shouldn't be a problem) I think it would make an effective brake. 

As far as a drawing program goes there is some 3d modeling software available for hobbyists for free. It's called fusion 360 and it's pretty incredible. It takes just a little bit of time to figure a few things out but it's not too bad to use. If you really like your drawing you could 3d print it directly from what you created.

Here's the link http://www.autodesk.com/products/fusion-360/overview

[pd]

Thanks for the link . I'm not sure my 2D mind is really ready for a 3D world .

Pete .

[carryall]

If I remember correctly, the band makes just makes contact with the outside of the clutch drum.  It works quite effectively.  The standard size is 4"