I want to wrap some ribbon along the bottom edge of a cake covered with SMBC but am concerned that the butter will permeate the ribbon.  Any suggestions?

Also what is the cleanest and best way to match the ends of the ribbon and adhere them to the cake?

the only time i have butter spots when putting a ribbon on a cake, is if there is BC on my fingers or if the icing gets on the front of the fabric. Then there will be a spot. Otherwise, I put the ribbon around a chilled cake and gently press the edges together at the back and I've never had a problem with the fat seeping into the ribbon. 

Even if its Swiss or Italian Meringue?

I don't think it would if it was an American or crusting type buttercream but the Swiss and Italian are much softer...

I always use IMBC. 

Just chill the cake first, then the IMBC will harden up as if it had crusted so you can easily adhere the ribbon.  Even chilled, the butter will saturate the ribbon and make it darker.  Try ironing wax paper to the ribbon first.  

AI hot glue wax paper to the back of the ribbon so the only thing that touches my cake is the wax paper. Keeps the ribbon clean and off the SMBC.

Ironing wax paper onto the ribbon?  Does the wax paper stick to the ribbon?