Don't all lathe taper attachments require that the cross-slide screw (or nut, or part of the cross-slide casting) be somehow disengaged from the cross-slide in order to operate? Otherwise, how could they work?
One variation is a 2nd cross-slide dovetail under the 'normal' one. During use of the taper attachment, the normal one is clamped tight and the lower one, separate from the screw, is freed to move. Another one I saw used a split nut for the cross-slide that could be removed. Yet another used a separate, solid compound slide that replaced the standard one with the screw in it, and had the taper ways clamped to the front of the bed rather than in the rear.
If one isn't planning on doing either production or complex radii & taper turning, a hydraulic tracer attachment is somewhat expensive to buy, and a hassle to set up and make templates for just a one-off.
Although it takes more time, simply using the compound to form a long taper in steps is an option that requires no special attachment.