Hey, I searched "fuel line vapor lock" and only found this thread. Hehe. Oh well. I just had Mark_T suggest looking at this and another thread to diagnose what may be causing my own "hot summer day starting issues."
Just wanted to tell you: I have the same problem, but my car throws a CEL and code 0446: EVAP purge valve faulty. I replaced the "EVAP canister shut-off valve" thinking that was the correct part, but the CEL came right back on after a few days. I just ordered part # 996-110-129-05-M100, the supposedly correct purge valve, from my favorite parts place, Parts Heaven (800.767.7250), for only $50 (used).
Here's my thread:
http://986forum.com/forums/boxster-general-discussions/25572-99-engine-dying-after-normal-startup.html#post220812
I'll post on here and my thread if the replaced EVAP purge valve will indeed solve your problem.