I glued a magnet to each weapon mount on the titan, so far just using white glue as an experiment. When I glue these permanently, I'll make a point to glue the bottom ones first, then the top ones. The problem is that the magnets are strong enough that they attract each other through the plastic shell, and it is hard to get them to sit straight while the glue is drying. I think the one on top will be easier to hold in place.
I glued a little washer (also from Radio Shack--they have a bag of mixed washers, including 20 of the little ones, for $1.49; there is also a bag of 40 small hex nuts for the same price--those might work better if they have more metal in them) to each mounting point on each weapon. Each arm has one magnet end and one washer end.
They do hold pretty well, though the armed weapon pivots a little. I think the nail head I experimented with first held better to the magnet, but is _really_ hard to cut flush. Maybe the hex nuts would work better, or maybe if I glued two washers instead of just one.
I just realized that the washers (or hex nuts, probably) aren't optimal, because the hole in the middle forces the washer over to one side, since it is the metal that is attracted to the magnet. I either need to find some small steel circles or a way to trim off the nail heads I have.
More magnets would be great (even with a weapon attached as a handle, they definitely resist being pulled apart). But that would approximately double the cost and increase the space between the mount and the weapon. I'd also have to make sure I got the polarity right!
[Later] I think I've decided what I'm going to do. I'm putting one magnet on each weapon mount on the titan, plus one on each end (paying attention to polarity) of the arms. That gives extra strength to the arm, so it doesn't pivot. Each weapon will get one washer. This seems to be enough, and is much cheaper. Any weapons that aren't steady enough will be given a magnet.
Here are some pictures.
A titan with weapons mounted.
Same titan with weapons off.
The weapons alone.