Place Parts on Assembly

Hi,

I need some parts that I want to place with some positions relations. Per example the distance d between part 1 and 2 I know I can use a mate but I need that both are colinear with the centerline I designed. How can I do that?

https://www.dropbox.com/s/xz794mvc5ln9edi/Untitled.png

Thanks

SolidworksParts And Features