1) Do you think that this will adversely affect my performance on the test day with a fifth section (because of endurance issues);
I think in your case it certainly couldn't hurt then.
2) is there any way to mimic that fifth section? Should I just find a random LSAT section to take alongside the actual preptest just to get used to it?
Doesnt matter. In the worst case you could use an old section from some test you've already done, as long as you're mentally engaged for that extra 35 minutes it's good enough.
Admittedly, I've mostly been doing PTs without
the experimental section. However, I also don't give myself a break between any sections of the test. I think most people are compelled by a fear that the 5th section will reduce their test endurance, so they add it as a precaution to avoid a potential loss in points. I think ultimately it's up to personal preference. As long as you're following strict time contraints when PTing your score will probably yield a pretty good representation of where you are.
But of course, I'm just as superstitious as everyone else on this site and I will be adding the 5th section to my final PT of each week leading up to the test.