Reverse Read/Write on arrays

Is there any standard'ish way to io:Read / io::Write on an array in reverse? That means starting at the end, reading/writing towards the front. Caveat: I really want to do this in-place not copy/reversing an array later in many cases only reading the first bytes (at the end), I need this for flipbase64 encoding. I checked out Cursors for this but they can't be reversed. Any other options?

No, not built in, but it would not be too bad to write your own.