Aron Paul did mention he'd been approached to be in the series but it fell through. Not sure how it would work as he's going to be 16 years or so to old to play himself, he's what 16 or 17 at the start of breaking bad, and BCS takes place 6 years before so he'd need to be 12 or so.
Plus Walt and Jessie had never met him before, so they'd have to play secondary roles, ie in the background or just connected to a main character.
They may get mentions ie a guys arrested with drugs and he mentions he bought them from a kid called Jessie, or someone mentions their kids enjoy chemistry with that nice Mr White