CMMN - 1 of n tasks pattern best practice


I have a CMMN question. Say I have three discretionary task options, ie the options may be send by SMS, send by email, send by letter (these are not the actual options, just examples). Hence I want the knowledge worker to choose from one of these options which triggers a process to complete the task.

Hence how can I use sentinals or other such that as soon as one of these tasks is initiated, the other two become unavailable? Would I have to use if-parts based on a status variable or is there a more elegant method?