Well i did this about 2 days ago and the easiest way to do this its with Inter Milan in Serie A
why?..cause you're only playing 3 cups (tournaments) in the season. To make it even more easy... this a matter of an hour, two top.
First - Get rid off all the players below 80 transfer them to another league, preferably not Serie A or B.
Second - Add some players with 99, i would recommend 8 DEF 8 MED and 4 FOW
(consider to use all your created players to get more achievements, and you will see this as an investment.)
Third - Simulate most of your season, cause with your created players your chances of losing are mostly none.
Fourth - I do recommend choosing to play the Final on the Italy Supercup and Coppa Nazzionale,
Fifth - Take a look a the table just to avoid any last minute second spot, also check your results on Coppa Nazzionale remembers you have to play home and away.
This way at the end of the season you would have won the Trebble.
Hope this helps someone.