Offhand? Wood shop joke anyone?
I would use these...
http://www.premierwood.com/ImagesCac...wel-I22357.jpg
Use a flat surface from a straight piece of wood like a high quality 2x6 and lodge the dowel into place on the plank using screws at each end to hold the dowel in place. The goal is to basically attach the dowel to the flat surface as a guide for when you go to do the sanding.
Use one of these - beg and/or borrow one as you see fit...
Amazon.com: - Wilton Combo Bench Belt and Disc Sander, Model# 4002: Home Improvement
The model and make does not matter, but you will want to be able to use the main plank as a guide to establish the first flat surface using the belt sander.
Use the sander to create a flat surface on the dowel at a right angle relative to the guide of the sander. The exact depth of the sanded surface with be relative to the size of the dowel.
The dowel can then be removed from the plank once the first plane has been cut. Rotate the dowel onto the flat surface and sand each face down to match the first cut depth. You do that until the dowel has 4 flat surfaces - four sides of your dice.
That will give you relatively equal grains, rounded corners to personal taste, and weight of wood for the dice.
Once you have the four planes shaped, you can mark the dice for cutting. Mark each die with independent measurements with gaps between each die to create accurate dice. Use a saw of your choice to out the dice.
The edges of the cut dice will have to be hand sanded to match the rounded edges of the dowel edges, but a Dremel tool should be able to handle that without any issue.
That would be my best bet, anyways.