I took a quick look through the source codes of the service object and I don't see anything that specifically handles or parses multi-value fields, it's just setting the input to the User's AD property as far as I can see, so I don't think you're going to pull that off in any case. Of course, I might be wrong since I'm not the one who wrote the codes, so don't fully take my word for it and perhaps post this question on the service broker page itself and the author will get notified and might provide you with an answer there.

Alternatively, although I'm not sure how the full implementation of your solution is with regard to using that service broker or smartobject, but since you know that's a multi-value field, you could handle that particular field seperately and do your own parsing/splitting and executing the smartobject for each value. It might not seem like the most efficient way, but it should work.

Hi Everyone. Thanks for the responses. I just wanted to follow up to let you know I ended up using the following community resource to help me handle this issue:

http://community.k2.com/t5/K2-blackpearl/PowerShell-Service-Object/ba-p/1025#

I set this up as a service type which will run a Powershell command. After unzipping the files I copied the Powershell directory to the root of the ServiceBroker directory:

E:Program Files (x86)K2 blackpearlServiceBroker

and then copied the files in Powershell/bin/debug to the root of the blackpearl ServiceBroker Directory which allowed me to Register a new Service Type from the drop down. 

After creating a SmartObject from this new Service Type within my K2 Studio workflow I passed the set alias command:

Set-ADUser -Identity <user_name -Add @{proxyAddresses="smtp:<user_name>@emerson.edu"} to this SMO.

Worked like a charm. Thank you to the Community for this resource. I look forward some day to learning how to write my own service types like this.