Tax on Freight

We have a situation where we want to tax freight at the same rate as item  or in some cases at a reduced rate. How can we achieve this using standard functionality in EBiz tax

In 11i we achieved this by using price modifiers and by using DFF's

Is there any way we can incorporate PL/SQL code in Ebiz tax . In the 11i instance we handled all the country specific tax computation with PL/SQL code. Is it possible to do that

in R12