What you want to do is run a bolt from the opposite side so that you have a stud sticking outwards. There's two ways to do it.
Method A: You'll need to remove the entire casting from the drum. Four screws in a diamond pattern on the interior of the drum.
Get an 8mm bolt from the hardware store and drill through that casting all the way; if you have an 8mm tap run that through the drilled hole. Then from the back side of the casting you'll need to insert and tighten that bolt so that the threaded part of it is protruding outwards.
Once you've done that much then you'll need to get a grinding wheel and grind the head of that bolt down a bit so that it becomes flush with the contour of the casting.
Method B: Doesn't require a grinder or removal of the casting. Get an 8mm STUD bolt and a tube of Loctite RED, the permanent stuff.
Thread the stud into the hole before applying the Loctite, to make sure it will cinch up, as in there's still a bit of thread left for it to grab onto. If it feels like you can get it to tighten up and stay in, then pull the stud back out and add a couple of drops of Loctite to it. Tighten it back up with your fingers and a gentle final twist with a pair of pliers... let it set for an hour and then reassemble your bass drum spur using an 8mm wingnut, like on a cymbal stand. If this doesn't work then you'll need to resort to method A.
The wingnut scenario is a much better way to fasten spurs to the drum, as if they strip out it's far easier to replace them than having to fix a stripped out casting.