Mating a part so that it slides through a groove?

Hello guys,

I'm a bit of a novice in solidworks, so my problem is very easy to deal with I hope.

I'm trying to mate a part such that a circular extrusion on the part slides through a L shaped groove on another part. I've attached pictures to show what needs to slide through what groove.

Since the feature sliding through the groove is a circular extrusion, the part must be also be rotatable about the circular extrusion. (Compare the rotational position of the part in the 'start position' and 'end position' picture for a better explanation)

What can I do to achieve this? I have tried the tangent mate but I can only assign it to the _ of the L groove or the |, but not both.

Help very much appreciated!

SolidworksAssemblies