Is there a way to get around this using a single regex or without resorting to pack() or am I better off just running through each character in a for loop with substr and converting it that way?

pack() is by far the fastest method of doing so, and a regex is most likely to be the second fastest method. But you want to dismiss both, and it's not clear to me why. substr() might be a "best of the rest", but does it really matter?

Abigail