Not changing whitespace in certain elements

FreeBSD uses tidy to clean up DocBook-generated HTML.  For example,
   tidy -wrap 90 -m -raw -preserve -f /dev/null -asxml  book.html

But some of the output is from <programlisting> elements, which may 
contain tabs that should be kept verbatim.  Here's a pre-tidy example 
with added line numbers:

  1  <PRE
  2  CLASS="PROGRAMLISTING"
  3  ><TT
  4  CLASS="FILENAME"
  5  >sys/boot/i386/boot2/Makefile:</TT
  6  >
  7  boot2: boot2.ldr boot2.bin ${BTX}/btx/btx
  8          btxld -v -E ${ORG2} -f bin -b ${BTX}/btx/btx -l boot2.ldr \
  9                  -o boot2.ld -P 1 boot2.bin</PRE
10  ><P
11  >

Line 8 starts with a tab, and line 9 starts with two tabs.  This 
particular example is from a Makefile, where tabs are significant.  Left 
alone, the text can be copied from the browser, and the tabs are obvious 
from the highlighting.  But tidy replaces the tabs with spaces.

Is there a way to get tidy to leave whitespace alone inside this class 
of <pre> elements?

Thanks!