automation drawing, how to make long lines or curves

I want to draw some automation for a parameter in an effects plugin and I want to have the parameter values change/cycle gradually over the course of four measure cycles, or eight or sixteen or whatever, using, say, a sine curve. Documentation says I can make the curve follow the snap settings, but problem is: drawing shape only goes up to one measure in length, regardless of how long I set snap. I can only set snap longer than a measure, by the way, by using seconds or ticks (or frames or samples)--which is a bit weird but okay--and PRV honors those longer values when placing, say, midi notes.  Automation drawing shapes do not go past one measure. Does anyone have an alternative way of drawing or painting or copying in "long form" automation curves for a plugin parameter? An alternative, that is, other than drawing the automation by "hand" (mouse) or recording controller movements.