The Howie Glatter tuBlug™ is the answer for those wanting to Barlow-collimate their primary from the back of the scope, but have a solid tube Newtonian or don't want to slide up their telescope shroud.
It is a Blug (Barlowed laser plug) containing its own lens and shadow screen that fits within a side cut-out tube, the combination being known as a tuBlug. Like the collimator self-Barlow attachment or the Blug, it uses the Barlowed laser principle to project a silhouette shadow of the primary mirror collimation mark back onto its white screen, where the shadow is centred to collimate the primary. The tuBlug comes in 1.25" and 2" sizes, fits any focuser, and can be used with any well-centred laser collimator.
Unfortunately, the standard Blug which fits to the inner end of the focuser drawtube inside the telescope, cannot be used as a tuBlug because it must necessarily have a shoulder which seats it squarely against the end of the drawtube. The shoulder will be larger than eyepiece diameter, which prevents the Blug from fitting in the side cut-out tube.