It's actually quite easy to setup a private match, which keeps out the rift raft.
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1) Boot up GT5 and enter GT Life
2) Click the community tab
3) Your PSN should already be selected, if not select it now
4) Move the cursor over the coffee cup
5) Hit X followed by join
Setting up Regulations
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1) Goto Regulation Settings (Far right side in your lounge)
2) Power Restriction (should one be needed)
3) Weight Restriction (should one be needed)
4) Tire Restriction: Sports Soft
5) Place a check mark next to all 5 bottom boxes (Skid Recovery, Driving Line, Active Steering, TCS, ASM)
6) Hit ok
Setting up the Event
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1) Goto Event Settings (Middle button on the far right)
2) Set Laps to 1
3) Boost should be set to Off
4) Penalty should be set to None
5) Hit ok
Setting up the Course
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1) Goto Course Settings (Left button on the far right)
2) Select Host Picks
3) Course should be set to Special Stage Route 7
4) Weather should be on Sunny
5) Check the little box next to Fixed
6) Hit ok