Is it possible to reduce the diameter of a drill bit?
I would suggest that you look a little farther. Drill bits are available in many more sizes than you mentioned. One big supplier on-line, McMaster Carr shows available metric sizes for heat resistant cobalt steel jobbers drill bits in all of the following metric sizes:



If you can find access to a supplier that has drills on the numbered gauge scale or the lettered scale they cross reference to metric sizes as shown here: