That is interesting. In reality, you seldom see fire blocks anymore. Occasionally when there's a very high wall. And they were never used for rigidity. Though there's some obvious merit to it, once you put on sheathing (that is, the sheet wood placed on the outside of the home), drywall, or plaster lath, rigidity is not a problem.

In the US, you can get long flexible drill bits. Since he's coming through the top plate anyway, he can just continue that hole by using an extra-long drill bit, drill-bit extension, or, potentially, series of drill-bit extensions.

Alternately, if it is wallboard of some nature (as opposed to plaster), repairing holes is really quite easy. Cut your hole cleanly, keep the cutout, get a couple of thin pieces of wood (shims, singles, etc.) and put them through the hole into the wall and screw them to the inside of the wallboard. Then put the cutout back in the hole, screw it to the wood you just put in, spackle, and paint.