What makes you think aer lingus would want to lease out an A330 at all, let alone at the times when required by the DF.
Once they get the open skys agreement sorted, they will be looking for additional aircraft, not looking to lease out a/c. The old business model of busy summer / slack winter is no longer acceptable. Aer lingus like ryanair etc, are moving to the business model where you have to make all of your assets economical 24/7/365. You saw what happened when the wind blew one 330 into another. It really screwed their schedule for days. So if you want to work in a lease arangement, it would all have to be aggreed in advance to work in with aer lingus' schedule, which i imagine would hardly suit the aer corps. And you can be sure aer lingus will make you pay for the privilage.
So what would be the most economical?
Surely the question of whether we need/want the G4 and learjet is a simple matter of economics.
If a large business can justify a biz jet for themselves, then i can imagine we as a country can.
Im not saying we do need them, i dont know, but surely some bean counter some where can let us know.
I know we all feel alot of the trips made by the gov are just jolies, but they will make those journeys one way or another. So what way is the most economical to the taxpayer....