To start with, I generally try to solve mapping issues with a pattern of built-in functoids. If it doesn't work, then I use this forum and Google to find suggestions before resorting to calling everyone I know. I've stayed away from that option for months, but it's always there.
After I exhaust my options or figure out that the pattern is too unwieldy, I head to C# and a quick windows app with simple logic in a button. If it’s 3 lines or less, I’m happy to use a script. If it will possibly be used again, I build a custom functoid. Recent additions were DateTime conversion (any localized .NET acceptable DateTime format that gets converted to xsd:dateTime) and a RegEx validator so I can return an error on a particular field.
You can build a library of custom functoids and refactor them as needed. Just remember they need to be deployed ahead of any application that uses them.