What I've had to do in such cases is to set a breakpoint with the condition.

e.g. if I have

%hash=(1,2,3,4);
while (1) {
  print "Something...\n";
  ===cut===
}
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you can put in b 3 $hash{1} ne 2
In a real scenario you may need to run to after %hash is populated to find out what the value is