I'm afraid it is not possible. Please someone confirm, but LCY has very strict noise regulations. Most airplanes flying there are 146s/RJs and some modern turboprops. As far as I know, although 737s are "stage 3" engined, they do not meet the very limited exigences of London City Airport.
Unless... wait a minute:
I don't know if any smaller ones of the CFM56 series jets (are these ones exactly?) would meet these regulations, but this would mean EZY placing his next 100 unit order to A319s/320s, and leave the 737s for the Swiss subsidiary.
Hey, I must admit that at first it shocked me, and I found your thought interesting. Then I remembered the noise regulations. And this made me think of the tax exemption for CFM equipped 32Xs in Switzerland thanks to low noise and exhaust emissions.
I must confess I made a fantastic mix of suppositions, but the way U2 is expanding fleet and destinations... Who knows?
Low low fares... directly to city center instead of 55-mile away Lutton? Hmmm... if Stelios is reading this... who knows!!!
Έλα, ρε Στέλιο, κάνε κάτι μεγάλο και εντιποσιατικό!!!