One of the reason I like Pt/pd printing (and carbon printing) is the fact that burning/doging (d&b) is difficult. It means that I must see more intently while photographing and compose for photographs that do not need d&b. This has become part of my methology and philosophy of photogaphing. It is part of the reason I work with only camera negatives.
That said, I have done a 15 minute burn using a piece of cardboard with a hole in it, but my particular light set-up minimized the amount of UV that my eyes were exposed to. I have also pulled the printing frame partway out of the light exposure unit to burn one side of the print. Perhaps one neg out of 20 of mine can use a little help like this.
Some of my exposures can be 30 min to an hour -- which means that a 100% burn, while not impossible, is impractical.
But some possibilities of b&d are possible for those who wish to. Those making enlarged negatives (either traditionally or digitally), can take care of any b&d at the time of making the enlarged negative.
Another possibility are masks laid on top of the glass of the vacumm frame over areas needing dodging. I remember reading of a photographer creating masks by laying material (rubylith, I believe) on a piece of glass that is then set on top of the printing frame during exposure. He was making silver prints, but it would work for pt/pd also. The mask was kept on file for whenever he re-printed the image...a very repeatable method of dodging.
Another way (but a bit more involved) is to position lights in such a way as to unevenly expose the print. I remember seeing AA's hort. 8x10 enlarger. The light source was a series of bulbs -- with the outer bulbs slightly closer to the neg, thus burning in the edges of the print a little. Once, I had a tube mal-function in my set of BL tubes and I used it to do a slight "dodge" in the center area of a print.
Have fun!
Vaughn