my workaround is to attempt repeatedly to initialize the serial object if the initialization fails.  basically:

1. public void initSerial () {
2.       try {
3.             serial = new Serial(this, Serial.list()[0], BAUD_RATE);
4.             serialInited = true;
5.       } catch (RuntimeException e) {
6.             if (e.getMessage().contains("<init>")) {
7.                   System.out.println("port in use, trying again later...");
8.                   serialInited = false;
9.                   Timeout retrySerialTimeout = new Timeout(this, "initSerial", 5000);
10.             }
11.       }
12. }

that Timeout class is my own class; you can use any method you want to re-try Serial initialization (e.g. a frame counter in draw()).  the serialInited boolean is a flag i check in draw() -- if !serialInited, i just draw a big red X.  once serialInited = true, i know Serial was successfully inited, so i continue on with my program.

just a little tidbit in case it helps someone else down the road.