You could try to create a dynamic plot, like this one whit shiny. But instead of the user selecting the number of points (as in the example of shiny) you could select the value of the rv that has the smaller number of values.

You could try to create a dynamic plot, like this one whit shiny. But instead of the user selecting the number of points (as in the example of shiny) you could select the value of the rv that has the smaller number of values.

In other words (from comment), plot a series of surface plots (or 2D density plots) of P(X,Y,Z=const).