I use OmniGraffle on my Mac and set about making up some hood designs. I haven't put any card through the printer yet, just been using coloured paper. The effects are encouraging and I suspect that with card the effect will be fine. Easy to make too! I've saved six different hood designs as a pdf should you wish to try things out yourself.
You'll notice a couple of rings on each hood design. These are 80, 77 and 52 mm in diameter. My lens is 77mm so I cut down to the second ring and then fold over. I then user an elastic band to secure the hood in place. Haver a squiz at the image to the left.
I've been playing with different coloured paper, but think a stiff black paper or thin card would be better. However, for the purpose of showing you how the hood sits on the camera it's probably better than black.
Here's a few images I took using black bokeh hoods. Have a play and let me know how you get on.
Oh, it'd be a good idea to ensure you have a filter on your precious lens prior to playing with the bokeh hoods.