Here's one method:

perl -e "$s='OOO....MMMM..IIIII';$s=~s/(.)(\.+)/$1.$1 x length($2)/eg;
+print $s,$/;"
#            OOOOOOOMMMMMMIIIII
[download]

Or more appropriately for here:

perl -e "$s='JJ..A....PPPP..HHHH...';$s=~s/(.)(\.+)/$1.$1 x length($2)
+/eg;print $s,$/;"
#            JJJJAAAAAPPPPPPHHHHHHH
[download]