, well, since you asked...
I figured I'd just pack grease into that cavity, so I hooked my grease gun up to the hole. I figured that once the grease filled the cavity that it would blow the out around the nozzle. This was so simple and cunning plan that there was no way it could fail.
Sure seemed to be taking a long time to fill that cavity, but I figured the grease gun was just not squirting that much grease per stroke. The pumping continued. I began to think that maybe it was going somewhere and, sure enough, it had traveled up the frame tube to a weld vent by the sub-frame bracket and had just started coming out.
I sat back on my heels and figured that it hadn't been that great an idea but no harm was done, really, and there wasn't shit I could do about it anyway.
On samuel's bike we used a chain lube with a tube on the spray head to fog the inside of the cavity, turned the bolt 180 and fogged it again, then covered the holes with 1/2" rounds of electrical tape and put a shmear of RTV over the tape.
The issue that I was trying to address is that the bolt is always greased before it is put back in but quite a bit of that grease is scraped off when putting the bolt back in. That leaves the bolt rather unprotected. And, of course, those holes need to be closed.