Isolating track after ballasting?

[RobertInOntario]

I have a small DC-wired HO (or British 00) layout that has two loops of track. The outer loop is isolated into two halves via plastic (insulating) rail-joiners so that I can stop one train on one half while still running another train on the other half.

The inner loop, however, does not have any isolated sections of track. I'm now thinking that it would be great if I could break the track into two sections via these plastic rail-joiners. Only problem, most of the line is already neatly ballasted, especially the sections where I'd like to add the rail-joiners!

Is there a quick, easy method of adding plastic joiners (or something smilar) to ballasted track? I don't want to get into ripping up my nicely-ballasted track, making a mess of the scenery, and relaying the track. I think the rewiring part would be fairly easy (thanks to soldering) but the track/plastic insulators part could be tricky. For example, is there a way of simply sawing through the track with an Atlas hobby saw and then inserting small bits of plastic?

Thanks in advance,
Rob