For anyone having trouble attaching all those swords you get with the BaC Marines, here's a solution that may work for you.
You can cut a small notch in the back of the sheathe of the blade, this will allow the sword to 'slot' in to the power cord coming from the power pack mount on the rear of the Marines torso. Allowing you to better line up the two spots on the sheathe were the backpacks lower vents should rest.
Another option, is to simply carve or file off an angle of plastic from the sword sheathe. This is both neater and works better depending on the rear torso you're using. (Remember, watch your fingers!)
Two swords ready to be attached
You'll notice the fit is a lot tighter, allowing you to match up the two vents with the sheathe.
I actually panicked a bit, I wanted to get this article out as soon as I got my BaC box (on release day) as I dismayed at fiddly bits being left off, because they're fiddly. Hope this helps make the swords an option you want to attach to your models rather than leave off because it's a hassle.
Happy gaming!