I've found that after I finish an invasion, when I've won, I press skip while
it goes through the prizes. Then when it goes to connect to my facebook to 
ask if I want to post about my win, I hit the top right corner over and over
again (where the x's are to get out of the boxes). I keep pressing it and 
don't stop until another invasion pops up. I've gotten up to eight times in
a row before.