Question on past earnings

I am a Working Holidaymaker here and my visa expires end of November. I am considering applying for the HSMP since I am under 28, have a BSc and can also claim 2 years graduate level experience from my country (2002 - 03) because I was working on graduate level jobs while in university and graduated 2003. But I will still need a few more points to qualify and that is where the question about the past earnings come in. I have not really worked in my relevant field (IT) since I came to the UK (about 19 months now). Can I claim points based on past earnings in my home country between 2002 and 2003 and explain that I have not really been in a regular work pattern here in the UK since my main reason of coming is to be on holiday and just take work incidentally to my travels around UK where possible (just as the working holiday maker program was meant to be in the first place). Hence I will not be able to present any proof of earnings for UK work (past 12 months) cos of irregular work pattern and not enough money earned to qualify in UK.

I have a few professional certifications in IT and I have had some job offers but because my visa will soon expire its getting a bit difficult. Please advise me on how I can present my case and score points on these earnings that are over 2 years old.

Thank you.