The answer if sort of in the question. But if you meant you want something more genereal:

s/(["'`])/'%'.unpack 'H*',$1/eg;
[download]

Or for every not alphanum char (and not quotes only):

s/(\W)/'%'.unpack 'H*',$1/eg;
[download]

Or perhaps you only want it for chars that can't be in a URI:

s/([^\w;\/?:\@&=\+\$,\[\]\-\.!~\*'\(\)])/'%'.unpack 'H*',$1/eg;
[download]