Trust me mate, use 5w40 oil and you won't have no trouble whatsoever... 5w30 is just a marketing ploy and no amount of additive package will save your cams from eating themselves- the dealer only specced that servicing interval due to being attractive to first time buyers- they only service the car once in their possession then they pass it on when the car is 3 years old ! Also dealer does not give a damn about 2nd hand buyers, if it brings them more work then it's all good !
Also think about all that ash held in suspension by the thinner oil, it will clog the oil filter quicker then the bypass valve opens and all un-filtered oil is pumped trough the engine- i have never seen cars on standard servicing intervals worn more than cars on Longlife servicing...