I have a customer who'd like a three tier cake put directly on her cake stand, rather than having a cake board/base. I normally would put a dowel down through all the layers into the base cake board, but that wouldn't work in this case. Will the cake stay on the platter? Should I use a single cake board on the bottom and duct tape it to the stand? 

Do you mean she doesn't want a cake board to show when you place it on the stand? Or she doesn't want any cake board at all? The latter doesn't make logistical or practical sense. The former is easy fixable. 

Two solutions you might consider:

1) use a thick base board (e.g. 1/2 in Painted Masonite or foam core with ribbon trim) that is considerably wider than the top of the cake stand, so it becomes the "top." 

2) use a base board the same size as the cake stand, assuming the stand is flat. That's what I did for the cherry blossom cake in my gallery. I also drilled a 2-in hole in the board to accommodate my cakesafe. At the venue, I just slid it onto the stand (a Sarah's Stand). 

I struggle with this issue - please post what you come up with!

I would find out why she doesn't want a board. I had a customer ask for "the smallest board possible so that the ugly silver board doesn't show" and when I told her I cover my boards she was fine with whatever size I used. I probably would not agree to stacking a 3 tiered cake without a board. It'd be different if it was a single tier birthday cake.

She's got a rectangular stand that has curved corners. She doesn't want a cake board to show. There will be a silver rhinestone ribbon, which I know can cover the bottom, but since it's tiered, don't want the bottom tier to appear much taller than the other tiers. I think I'll just put a single cake board underneath, and do that. Thanks for all the suggestions!

Will you be stacking it on sight? If not, you'll need more than just a single board.