Odd, this issue has been buzzing me... It looks like you have entities already in place, at the angles you want this new item to be, so I would try something along the lines of adding the new item to the other component definition as a sub component. If the 'angled surfaces' are not components make them so. Do it once, or twice, depending on how many angles... and you are done. My case required two, even though it looks like more.
faces into components-10.JPG
faces into components-7.JPG
See:
http://forums.sketchucation.com/viewtopic.php?f=79&t=40874&p=404847#p404847