How to clean object files in a custom folder with PB 4.2?

Hi,

whenever I add a feature to the platform which will be build outside the
_WINCEROOT folder, a clean does not delete the object files created by a
previous build.
For example, my _WINCEROOT folder is D:\WINCE420 and I have a feature with
the following build method:

BuildMethod
(
Step ( BSP )
CPU ( "x86" )
Action ( '#BUILD(SOURCES,"D:\Projects\OtherLocation")' )
)

the object files are created at
D:\Projects\OtherLocation\obj\x86\[debug|release] and are still there after
a "Clean". If I move the project to somewhere beneath the _PROJECTROOT
folder, the object files seem to be deleted after a platform build (I
couldn't find them after a platform build, but the target exe file is
successfully created).
Where does PB 4.2 create the object files and how can I obtain that the
object files are created in that folder even if the source path is anywhere
outside the _WINCEROOT folder?

Thanks in advance.
Markus Bauer