I could be wrong but I'm not sure the actual accounting record would touch the P&L side (until the amortisation is accounted for). If they paid all £12m upfront the bank/cash account would take the hit, but you'd have an asset appear in the accounts. Even if they didn't pay for all £12m upfront they'd most likely record the asset in full and then have a liability account (Liverpool) which would be reduced if and when they paid (using the bank as the other side).
But as @ScarBorosays the amortisation (and the expense - P&L side) would still only show as the original cost split between the contract length in this instance £2.4m regardless of when they actually paid.
Under normal accounting standards for intangible assets, transfer fees are amortized on a straight-line basis over the period of the players’ contracts. This was how Derby got into trouble by assigning a residual value to reduce the annual amortized cost to the club. Let's say you are allowed to defer the payment, the costs would have to be assessed over a reduced period and therefore be higher in the out years, big risk if you don't succeed.
Surely depends how they account for the actual transfer fee payment, can’t remember if they put it through operating costs or not (and Cba to check right now). If the transfer fee is incurred in the P+L as it’s paid then there is definitely a FFP benefit to back ending payments.
It'll be a loan deal for a year as Mr_Maz says. If it's got any link to FFP then I can only think it's to help Fulham's FFP position for the coming year. I don't believe they've sold anyone for any serious money so far, and they would ideally want to keep the net transfer spend as close to zero as possible, as their wage bill will be higher than the parachute payments they receive. If things don't go as they plan this season then they will probably sell players next summer, which would balance things out for FFP and also cash flow, so the transfer of Wilson then will be fine.
If I was a Cardiff fan I'd read those paragraph's as Brown will probably be gone and Boro's rejected bid wasn't far off, it would be interesting if we sign him AND Kean Bryan. It would definitely add some depth to our left side especially if we're looking to play 5 at the back more often than not.