I recently bought a Spector MOUT sling for my underfolder AK. It works amazingly. You can easily seperate/attach the weapon and it allows the weapon to be used effectively with the stock folded.
Its a high quality sling that fits in an unobtrusive manner. I bought several other adapters so I could use this sling for a few other weapons. I personally think a single point is the best sling for a weapon with a folding/telestock and this is certainly one of the best. There are other single point manufactures and designs but I feel this was the most conducive to an underfolding AK.