IDOC in transformation step with multi mapping

Hello,

I have found this posting

Splitting a message into multiple Idocs

and now I am a little bit afraid that our planned process using BPM is not working:

a) XI receives an IDOC

b) XI continues with calling an external system sync.

c) Sync message response and IDOC are used to be merged into one new message M using transformation step (2 messages into 1 new)

d) send message M to receiver

Now I have read (see link) that IDOCs cannot be used in such multimapping steps. Is this true?

Can anybody give some information?

Best regards

Dirk