That is one way - loosen the nut with an AR armorer's tool, and replace the tube lock with an after market one with sling attachment points. I have an a new tube lock to do exactly that, but have not gotten around to it, so I cannot confirm that an AR tube lock will fit the Colt. Remember that the Colt does not contain a buffer, spring, ect. You can also purchase attachment points that clamp on to your accessory rails, and many butt stocks, including the Colt's, come with slots or attachment points.
TM