How to expand environment variable in compilation command?

Hello
Is there a way to make 0install/0compile expand multiple items in an 
environment variable into command line arguments for a program? A local 
feed of mine depends on boost headers:
<requires interface = '../boost/boost.xml'>
   <environment name = 'CPPFLAGS' insert = 'include' mode = 'append'>
   </environment>
</requires>
which works well when I use shell-command = 'c++ -I $CPPFLAGS 
$SRCDIR/test.cpp -o $DISTDIR/test' to compile but as soon as I have 
several dependencies injected to CPPFLAGS it fails. The documentation 
and example for <for-each item-from='...' separator='...'? > ... 
</for-each> wasn't very clear and I couldn't get it to do anything, can 
it do what I'd need in this case (for each item in CPPFLAGS append -I 
$item to shell-command) or is it for something else? Thanks
Ilja

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