You can use a Philips SAA1064 4-digit LED-driver with I²C-bus interface. It only needs two I/O lines from the processor, can drive the decimal points and each segment the way you like, so you can make all patterns you want.
Furthermore, the multiplexing is done by this chip, so this doesn't take time from your controller.
Look for the datasheet at:
http://www-us6.semiconductors.com/pip/SAA1064T

Search the net for software I²C routines, there are many sites where you can find samples.

Have fun with your project :)

Henk van den Broek