My friend Jerry and I designed and made a custom pen holder for the Cricut the other evening (mostly him , and I finally got to try it out, with mixed success.
He blogged about the build here:
While it fulfills the original requirement perfectly (hold a staples mini gel pen accurately), I realized I wanted something that would hold -any- suitably sized implement.
The fit and finish are outstanding, but as it turns out, the tiny hole in the bottom of the holder end up being the limiting factor and just doesn't leave enough room for adjusting pens up and down. Different pens have different profiles and tip sizes, and a colored pencil with that small of a tip went dull within just a minute or so.
So, much as I hate to hack off that pretty nosepiece, I think I'm going to try making it more useful by just hacksawing off the first half inch or so of the unit, leaving the whole thing just a straight tube down the inside. This certainly simplifies the design as well.
The thumb screw and close fit bore hold the pen well enough already that jaggies in the output are visible from the mechanical and software limitations of the system, and not from slop in the pen rattling in the holder. This should give me enough flexibility to use colored pencils better (they get dull really fast so you need to adjust more often), as well as mechanical pencils or any tool I could make out of a coat hanger or other thin rod or dowel.
Note: the easiest solution for using alternate pens is just wrapping thin strips of masking or metal tape around where you want the clamp to grab and works just fine. Unfortunately the pen cap cant be put on anymore with the tape in the way, and you have to do this with every implement you're going to use.