My son loves building with those blocks and so I got involved, too. I wanted multiple nubs, so I made those. I hope you like them as well.

In the future I plan on editing it to remove the holes as they tend to cause stringing and I also hope the bottom print better without a hole.. but it works and I have other projects atm. I also may include a version with preset supports.

Please print in TPU (I used Jayo TPU 98A - works great), as PLA will be too hard and it won't work.
And please paint some minimalistic supports one the nubs on the sides.

FreeCAD model for the daring.