How to dynalically set isSequential based on a varibale

Hi All,
In BPMN process, we want to set the isSequential value on the fly based on a variable.
First is it possible. I tried setting isSequential="#{approvaltype}" and even isSequential="${approvaltype}" in the bpmn:multiInstanceLoopCharacteristics element. But that did not helped.

Any help will be highly appreciated.
Thanks for the help in advance !!!