All depends on the block times and turnaround times but it isn't beyond the realms of possibility.
LGW-ACE = 4hrs 15mins
ACE-LPA = 30 mins
LPA-ACE = 30 mins
ACE-LGW = 4hrs 15mins
Turnaround times = 4 x 30 mins each
Report time before = 1hr
Total FDP required = 12Hrs 30mins
Max allowable FDP = 12hrs 45 mins (cabin crew reporting between 0800-1259 local)
Now, like most good schedules it looks good on paper, however in the real world I would say that you would be using discretion on that little day out.