You just need to reduce the clock frequency to apx 12MHz or lower.
Change the CPU frequency setting in the Makefile and add a
new configuration to boards.txt Information on the bootloader changes
I do is at
http://wiblocks.luciani.org/docs/app-notes/bootloader.html
I will be adding the information on the boards.txt updates
in the next few weeks.
All of my board run at 3.3V / 12MHz (see http://www.wiblocks.com )
In the next few weeks I am hoping to release my
PICO1-TR 2.1" x 0.975" ('328, TH components)
adjustable regulator -- can be trimmed to voltages from 3.3V to 5V
by changing one resistor.
(* jcl *)
www: http://www.wiblocks.com
twitter: http://twitter.com/wiblocks
blog: http://luciani.org