Don't be put off by offshore pilots struggling to get onshore jobs. I was told long ago that ME IR work does not mean you have the skills for onshore VFR work. Two very different roles requiring a different set of skills.
Traditionally the self improver route was, as you indicate, slow building of licences and hours as a flying instructors. It has worked for many of those now doing that elusive job you crave. But it was never easy and there always has been times of pilot over supply, usually followed times where the NS has drained the over supply. I guess now with JAR there is an even greater over supply as a modular CPL is cheaper to get than it was under the CAA.
I don't know the answer to your problem. You are not the only one in this position and most of those self improvers that now earn their money flying have been there too. Persistance and patience are needed in spades and I guess if you don't want to fly offshore, then an instructors course will be the only way to achieve your dream. Unless of course you can afford to build that experience yourself, in which case don't bother with a flying job - just fly for fun.