To answer the general question, you use /^(?s:(?!ending-regex).)*/ but for any particular case, there will be a more efficient way.

Update: I didn't mean to apply the //s flag to the ending-regex; should have been /^(?:(?!ending-regex)(?s:.))*/.

In your case, to do something like that you would need to switch to slurping in the whole file instead of reading line by line (by undef'ing $/). You may prefer to keep the code you have and just interrogate the return value of your ..:

while (<>) {
   my $inrange = /^\.subckt/../^\w/;
   if ( $inrange && $inrange !~ /E/ ) {
      print;
   }
}
[download]

The scalar .. operator returns a positive count if you are in the range. At the end of the range the count has "E0" appended to it, explicitly so you can check for this condition.