No, Fran... if you actually WANT the aftertouch possibilities for your RH (you want to impart vibrato with pressure from the RH) you can't stop the pressure in the LH from triggering it. All you can do is turn down the sensitivity until it takes more force than your LH is imparting to activate the effects. I usually set any aftertouch I use to it's lowest setting, so that this problem is unnoticeable as much as possible.

Lee, I imagine that setting your Velocity sensitivity fairly low (so that you don't NEED a lot of force in your LH to trigger what you want) on your LH sounds will help you to avoid this problem, along with setting the aftertouch sensitivity as low as possible (so you need a fair bit of force to activate it) will keep this problem from being too noticeable. Plus, as others have suggested, turning OFF the aftertouch reception for Parts you don't actually want it on.

If I were you, I'd spend a fair bit of time with the manual investigating how to control and scale both aftertouch and velocity (and, as you have the module version - correct? - the aftertouch and velocity capabilities of your controllers as well) before you get too worried about things...