Described are needleless injection systems and methods that involve features including one or more of a tissue tensioner and a fitting for attaching to a distal end of a shaft, exemplary embodiments including: an elastic sleeve sized to fit under tension about the distal end of a flexible scope, such as an endoscope; a non-metal, polymeric tube-like device being optionally attached to the elastic sleeve for delivering a therapeutic fluid to a treatment site within a patient wherein the elastic sleeve may include an integral balloon (tissue tensioner) feature that can be used to position the injection orifice of the tube-like device proximate a treatment area.