unicode ligatures and interrupting markup

Hi all,

For some Arabic text we need an underline to start (or end) halfway 
throuh a word. The <u> markup for that is interrupting the characters 
and therefore killing the required ligatures (writing variants of the 
characters). Would anyone know a proper way around this? Example in Word 
(they know how to do it):

[Y_YX'X2 Y>ZZ>[ _X*Z>[[]

Thanks,
Pieter

-- 
Pieter Lamers
John Benjamins Publishing Company
Postal Address: P.O. Box 36224, 1020 ME AMSTERDAM, The Netherlands
Visiting Address: Klaprozenweg 75G, 1033 NN AMSTERDAM, The Netherlands
Warehouse: Kelvinstraat 11-13, 1446 TK PURMEREND, The Netherlands
tel: +31 20 630 4747
web: www.benjamins.com