Just to clarify, you don't want to know how to make the filling - you want to know how to keep the filling from oozing out?
To keep the filling from leaking - make a dam around your cake layers (prior to filling) by using stiff frosting in a pastry bag with a large size couple.
http://www.wilton.com/wedding/makecake/fillinglayers.cfm
HTH
If that wasn't your question, sorry I couldn't help!!!
They probably get theirs premade in sleeves. Pastry Pride (I think that's the name) sells it, and I assume the grocery store just adds the strawberries to it, because the sleeve is just jelly.
You can find it online if you don't have a cake supply store in your area.
Quote by @%username% on %date%
%body%