SAP PI 7.3 with SAP BPM

Hello All SAP PI experts,

Currently the clients want to execute a scenario wherein they want a few messages to be merged into a single message before sending them to an external system. Since that is not possible without BPM and PI 7.3 doesnt have BPM installed (as in PO 7.31 onwards) we are thinking of suggesting them to install SAP BPM first and then PI will contact BPM and get the messages merged and forward it to the external system.

Is that possible ? would it be a good idea ? Kindly suggest as soon as possible as this is very important.

Thanks,

Ajeya G V