SmartObject - Pass Multivalue string

Hi,

How do you pass a multivalue string to the input property to a SmartObject?

For example, how do I pass in a collection of Roles to the UMUser - Get Users for Roles SmartObject:

I found an old forum post which suggests supplying in this format: 

<values><value>RoleName1</value><value>RoleName2</value></values>

I have tried this, nothing is returned?

My ‘Plan B’ is to create a hidden list view of the roles (if possible), then do a for each loop and pass in each individual row to the Get Role Users method. I know this may work but seems like to much hassle and less performant.

Thanks

(K2 5.3 FP23)