Place marker offset from robots position

edit

I am currently detecting an object using the Kinect and have the depth of the object. I am wanting to display this object in rviz by representing it as a simple marker.

What I am having trouble with is finding the transformed location of my robots position (with offset) to /map. i.e I want to do something like rosrun tf tf_echo /map /base_footprint + (0, 1, 0) (1m Y offset).

I have gone through the tf python tutorials and have successfully set up broadcasters and listeners I am just having trouble transforming a pose given an offset of some kind. (I can successfully transform between /map and /base_footprint but I cannot add an offset to /base_footprint)

I am sure I am missing something simple, just having a bit of trouble getting this going.