Custom Function to Prepend a Case Subject with an Account Name

Custom Function to Prepend a Case Subject with an Account Name

We use cases a lot. To submit a case you must enter (among) others:
Subject
Account

Is it possible to have a custom function prepend the account name into the subject. For example when creating case:
Subject = Testing
Account = Jones, Smith

Custom Fuction would then set subject to [AccountName] - [Subject] .... For example:
Subject = Jones, Smith - Testing

Thanks