I found a 3.5.9 patch to add a trash can dialog to set trash 
storage limitations. The dialog would look like this:

http://tokoe-kde.blogspot.com/2008/08/size-limits-for-trash.html

The patch did get submitted in the KDE bugzilla but never got 
merged into 3.5.x.

I converted the patch to TQt3 and added an option to populate the 
konqueror configuration dialog with a trash icon that should show 
the same dialog.

The patch fails to build for me:

/dev/shm/tdebase/tdeioslave/trash/ktrashpropsdlgplugin.cpp:226: 
undefined reference to `TrashImpl::trashDirectories() const'
/dev/shm/tdebase/tdeioslave/trash/ktrashpropsdlgplugin.cpp:141: 
undefined reference to `TrashImpl::trashDirectories() const'
/dev/shm/tdebase/tdeioslave/trash/ktrashpropsdlgplugin.cpp:61: 
undefined reference to `TrashImpl::TrashImpl()'
/dev/shm/tdebase/tdeioslave/trash/ktrashpropsdlgplugin.cpp:62: 
undefined reference to `TrashImpl::init()'

If you are interested then I have attached the patch to bug report 
1923.

Darrell