Tried and tested solution for this. It's weird so bear with me. You'll need 3 people for this method. Go into online mode with a team of the relevant star rating. When on the search/team management screen, change the controller settings to manual on everything, analog sprint on and auto switch off. Tell your partner to do the same. Now change the matchmaking settings to match your controls. This should match you and your partner everytime. Now load up the match, go 1-0 up and then get your partner to quit after 5 mins.
When in the finals, your partner will match with you if you are in any stage so long as they have progressed from group stage. To make it quicker, get your partner to use a third player to progress through group stage.
Credit to g77experience and see ultraamoeba's post in the 0.5-1.5 star achievement for this method. It can also be used in road to rio to win the cup, it's just a bit long swapping wins and buying extra matches and wins for each other.