Just put a condition above it that decides when to run the loop. Because conditions are read in top-to-bottom order, if conditions above the for each loop are false, it won't reach the for each loop.
In Porlo's case you'd actually want to do
+ Trigger once
+ For each ...
Or maybe
+ Start of layout
+ For each ...
(Putting trigger once below the loop has no effect, because things below the loop are repeated once for each iteration of the loop)