What is the recommended way to split messages in send pipelines?

I need to split a bizTalk message in the send pipeline. This is easy with disassemblers in receive pipelines, but doesn't work in send pipelines (makes sense).

So what is the recommended way to do it? The only easy way to do it is to write the outbound message to file, then reprocess it using a receive pipeline with a disassembler, and then send the generated messages through a outbound pipeline. Honestly, I don't need the additional roundtrip through the message box, but I don't want to create a custom send adapter.

Any other suggestions? Any easy way to save messages with multiple parts using the ootb file adapter?

While your solution is probably the best approach for this, you can also think about splitting the message inside of an orchestration (not the best practice) before the message even hits the send pipeline. The send pipeline is obviously designed for composition of messages and not decomposition so I would stay away from any custom code to handle this.

Here's a good article on debatching messages.