I'd be surprised if any additional dates were added to the European tour - given the prices, there are a lot of tickets still available.
I doubt a second night at the O2 would sell to an acceptable level for them.
For comparison, I bought 2 excellent tickets for the comedian Peter Kay at the O2 yesterday. Cost £146 for 2 (that's £73 each with those silly extra admin costs). Same thing would have been £400+ for Gabriel.
I genuinely can't get over how ridiculous the prices are. It's a really difficult economic time, and for a man who always places himself on the side of "right", this seems very, very wrong.
And this isn't just the call of the promoter - Gabriel could absolutely have stepped in and made them cheaper.
I hope anyone who has tickets has an excellent time though!