If you only put tape on the piano strings, you'll get a muted sound and that's it. Put a microphone on that piano, send that through a tape delay effect or at least an analog delay simulation (no digital delay...), and you'll get much closer to that awesome sound Brian was getting in the studio that day. The engineer even exclaims "That sounds wild!" on the tape, right?

I'm sure there is one, like a patch named "muted piano" or something, but I can't see how any synth could do that. Even a sampled sound of that...you're not getting the variation of low-mid-high strings. Or maybe someone has designed a sample/sound for that. Have they?
This stuff was found in avant-garde and experimental music from composers like John Cage (and putting the nuts and bolts on the strings), but one famous example of the muted/prepared piano in pop music around the same time was the weird piano break in "Something In The Air" by Thunderclap Newman, just a year or so after Brian's session. On that one, I heard they laid a blanket over the strings inside that piano for their effect. It really does sound cool.