$_ = join '', <DATA>;

# Add & to front of function calls without.
s/&?(\w+\(.*?\))/&$1/g;

# Add () to end of function calls without.
s/(&\w+)(?:\((.*?)\))?/$1($2)/g;

print;

__DATA__
&somesub('args');
somesub('args');
&somesub;