With house costing €450k, you would normally need 20% or €90k which would leave you with a mortgage of €360k
However, the lenders are allowed to make exceptions to this rule, and an exception might be made in your case.
AIB has a tracker mover product, where the margin is raised by 1%. So if you are on ECB +1% now, the €220k would be on ECB +2%, and the rest would be on AIB's normal rates.
Given that you will have this cheap mortgage, your mortgage will be affordable. AIB would love to get the extra 1% on the €220k, so they might well facilitate you.
The only way to find out is to ask.
Brendan