my $test = "Wherefore art thou, Ovid, you moronic chowderheaded shell of a ghost?  Give me my fleas and leaf.";
$test =~ s/\b(qu|[cgpstw]h|[^\W0-9_aeiou])?([a-z]+)/$1?"$2$1ay":"$2way"/ieg; 
print $test;

Output (split on two lines for legibility):
ereforeWhay artway outhay, Ovidway, ouyay oronicmay owderheadedchay ellshay ofway away ostghay?  
iveGay emay ymay leasfay andway eaflay.