Hi,
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.
The only possibiltiy i see is to generate the GS1 datamatrix using javascript. There are in the internet some code examples you could use.
Javascript can be executed inside adobe forms in the scripting area.
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