honestly it's still not possible to generate a GS1 Datamatrix with Adobe Livecycle Designer 11. There is even no other character combination.
I tried already many options.
An other option is to call a webservice vial scripting which gives you a image back with the gs1 datamatrix.
If you need a solution for SAP which also uses adobe forms you could ask software solution providers like in the link below.
They build a complete GS1 datamatrix image generator inside SAP.
SAP GS1 Barcode Generator - Europe IT Consulting.ch