I have used the stuff before, and it does work, but it is really really really close to the melting point of aluminum, and once it actually does start to bond with the aluminum, it lowers the whole areas melting point and can go poof in a hurry,s o you end up with a melted blob.
I have seen this as well when my kids were using it to make a frame for a robot, although, I haven't melted anything as of yet. I have a lot of experience soldering and it's really similar. The area needs to be clean and scuffed with a wire wheel or something similar. I would try to close up the hole as much as possible by possibly peening the hole shut with a small punch. The rod material will become liquid-like, but will also spread with some surface tension, so it only drips in my experience when too much is applied. As you heat it evenly, try scratching the rod against the surface. It is OK to leave the heat on while you do this. Do not leave the rod in the heat and try to melt it that way. The most important thing is that the work piece be up to temp. The braze is strong on the finished piece, probably even strong enough to bend and twist the part after you're done. Practice is important, because you won't want to try to heat it a second time as the low melting point of the material will cause it to drip away. Perhaps you could also braze it from the underside so that it can't drip inside.