A good comprehensive answer emerg000, I think you capture how difficult this would be to complete on a part time ad hoc basis. However there are some slight differences between the CASA system that you describe and the EASA system. There is a B3 license emerging, specifically for light aircraft, this is in effect a B1/B2 light. The experience and knowledge requirements are lower and so may be attainable over a reasonable time scale part time.
Also for clarification the B1.3 license is for Turbine Helicopters under both systems.
The Engineer License Guidance Document published by the UK CAA is a good read for the basic info regarding experience etc. I suspect with your backround and qualifications BCW that you would be able to go down the skilled worker route and have your experience requirements reduced to 2 years.