Weldment end caps?

No matter which direction I specify in the Property Manager when performing an endcap on a weldment, it always extudes the cap away from the part. I am looking to extrude it in so that the overall length doesn't change. Feel like I must be missing something, but I've looked it over a number of times and everything looks right. Any suggestions? I do a lot of tubing weldments and having to manualy sketch and extrude the caps eats up a lot of time.

Thanks in advance!

SolidworksWeldments