It depends on what wire you use, and how well you solder it.
Using thin multi strand means that the wire is unlikely to break, as it would do if using single core wire. The ends of it can also be crimped/flattened in the jaws of a pair of smooth pliers, and solder applied to the resulting tab prior to soldering it to the underside of the rail. It is unlikely that such a joint would break, if the rail was cleaned and cored solder was used.
As CA is going to have PCB track, then the wire could be soldered onto the PCB next to the rail, which would make things even easier.
However, if the wiring is to be buried subsequently in scenery and ballast, then it needs to be fully tested, and the track needs to be laid to the final plan - although with PCB track, that's pretty much the case anyway.
I realise that my suggestion goes against perceived wisdom, but there is no denying that being able to solder without constantly inverting the layout has its attractions: no back ache, and no molten solder dropping onto one's face when underneath the layout.
There is no reason for it not to work, and as I said, it has been proven on an exhibition layout, too. (Trevor described the wiring up as a very easy and pleasant process.)
The layout also features rodding on the surface, mostly under the platform which is screwed but not glued in place. Handy that, as an omega loop got displaced at Uckfield. I popped below with a screwdriver, undid 3 screws, and the repair was easily made.
Apologies for the picture quality - entirely my fault.