Extra work 20 hours per week for tier 2 ict: urgnt help need

Hi Guys

I really need an urgent help. Please suggest.

My situation:
I am a software professional in UK since Jan 2009 under Tier 2 ICT Visa. I have got job offer from RBS on contract through a consultant. There is an 'other' employer who has issued me a CoS for switching from tier 2 ict to tier 2 general on March 30, 2011 (under old rules before April 06, 2011). The 'other' employer has in turn signed contract with the Consultant to work with RBS as client.

The problem is that my switching to Tier 2 General is in process and is expected to be completed by end of May 2011. But I need to join RBS by May 3rd.

My Query:
I have read somewhere that I can work for 20 hours extra apart from my regular work hours on the same designation for which CoS has been issued. My question --
1. can i join the 'other' employer for 20 hourse per week work till my new tier 2 general in issued? the 'other' employer in turn can sign the contract with the Consultant to work with RBS for 20 hours/week? In this way at least I can start working wit RBS till my full visa is made.

2. is their kind of restriction on the 'other employer' for 20 hours extra work? can he be a 'other' employer, as in my case who will in turn send me to the client RBS?

3. My plan is to take leaves from my present company for Month of May every week for 20 HOURS and work in RBS as an extra work (for 20 hours).