It is possible with OpenType features, as described by Thomas Phinney using contextual alternates. Some other people have used that idea as mentioned here:
http://www.typophile.com/node/19625
Here is a basic code sample:
feature salt {
lookup rotate {
sub @set_1 @set_1’ by @set_2;
sub @set_2 @set_1’ by @set_3;
sub @set_3 @set_1’ by @set_4;
sub @set_4 @set_1’ by @set_5;
sub @set_5 @set_1’ by @set_1;
} rotate;
lookup rotate;
} salt;
There also seems to be a rand OpenType feature, but AFAIK that isn’t supported by any word processing software. More information about OpenType feature support can be found here: OpenType Features - How Many Programs Support Them?
If you want to know how to add OpenType features with the OpenType Compiler developed by Rogier van Dalen, do follow this link:
You can also use Microsoft VOLT to add OpenType layout features to your fonts.