A suggestion to get around this would be to put the drums on a Foot Pedal (FC7 sweep pedal) and fade them out (abruptly) when you want them to stop. This way you can continue to play the other sounds in the Performance without having drum sounds under each key.

To do this you will need to know how to bias the Volume of the drums to the Foot Controller. Lets use the Generation Performance as an example. It uses a DRUM kit PDR: Big Kit and 3 other sounds. What we will do is call up the BIG KIT PDR 017 in VOICE mode and edit it as follows:

Press Edit/ Common/ F2 OUTPUT
Set the Volume to 0
Press F4 Ctl Set Control Set/ SF1 set 1/2
Set the SOURCE = FC2 (04) Foot Control 2 which defaults to sending the foot control message which is assignable
Set the DEST (destination) = VOLUME
Set the DEPTH = +63

Store the BIG KIT to USER 016. the Volume of the drums are now biased to the FC2 controller.

Go back to the Performance Generation and substitute our new version of the Big Kit. This can be done from the main Performance screen by pressing F3 VOICE and setting the first Voice to UDR:016 Big Kit. Store the Performance.

Now when you want the drums to stop you can heel down the pedal plugged into FC jack 2 and the drums are gone but you can play-on undisturbed.

If you do not have an FC7 pedal you can accomplish the same thing using the FC4 or FC5 sustain type foot switch (FS) plugged into the Assignable FS jack.

In UTILITY F4 Ctl Asn/ SF3 Ft Sw
Set the FS = 7 Main Volume. Then bias the Drum Voice to the FS as above:

Press Edit/ Common/ F2 OUTPUT
This time set the Volume to 127 (because we will reverse the Depth parameter below)
Press F4 Ctl Set / SF1 set 1/2
Set the SOURCE = FS Foot Switch
Set the DEST (destination) = VOLUME
Set the DEPTH = -63 (this time minus 63 because you want it to work backwards).
Store the new Drum Kit and place it in the Performance as we did before. Now when you step on the FS the drums are out ... let go and they're back.

Alternate: Of course, if you have big hands you can always reach up and use the CS Slider - each sound of a Performance has a CS slider that controls the Voice volume via internal System Exclusive messages. And you can pull it down, but this method sometimes is not possible due to what you may be playing so I offer the assign a foot controller/foot switch methods. Hope that makes sense and helps.