For WiX 2.0, tallow is very limited; paraffin and mallow offer additional functionality.
For WiX 3.0, heat offers the same functionnality as tallow, a little bit better.
In my case I’ve used mallow source and modified a bit and used it, because paraffin needs 3.5 version of .Net.
You can use Mallow
or Paraffin tool to generate WiX fragments:
Getting started,
The pain of WiX,
A better tallow, Paraffin,
Download,
Paraffin for WiX 3.0