You can use TPIC6B595 shift registers to sink current thru the strings of LEDs that make up your segments.
Each 12V powered string, generally 5 LEDs, maybe 6, will require up to 20mA.
Each output of the TPIC6B595 can sink 150mA, so you can have 2 or 3 strings arranged to be as long as you want the segment, or strings next to each other for fatter/wider segments, and each shift register output can still handle 1 segment.
You'd then have a shift register per digit.
This board I make has 12 shift registers, fully populated it could do 12 digits. No multiplexing required, so the digits are nice & bright all the time.
http://www.crossroadsfencing.com/BobuinoRev17/
Here's another that supports just 4 digits - you don't have to add all the extra parts (3.3V regulator, SD card socket, RS232 driver, or even the screw terminals).
