The rectangulat plastic bubble tags are not magnetic, they are capacitive. They are deactivated by use of a magnet...that is what is on that pad at the checkout counter.
Unfortunately you need to sneak them past the entrance. Not really a problem...what you do is buy a largge number of items with them. Dremel tool bits always have them. If you luck out, then you have to get them out the door. Again, not a problem. Once you trigger the alarm, have the receipt handy and pull one item out, showing both to the clerk. They will then deactivate the one tag, leaving the rest active.
When removing the tags, do NOT peel. Cut them out. Peeling damages them.
Now you need to sneak them INTO the store with your friend. If the store only has exit sensors, you are golden. If not, you need to sneak them into the store. Hide them in a length of threaded pipe, complete with steel caps. You only need the caps on finger tight. Even a length of 1/4" pipe, easy to carry in your pocket, is sufficient. It must be steel with good fitting caps.
When your victim isn't looking, slip a few into his pockets etc.