Seeing as the FPGA doesn't have a Front Panel you can interface with, why would it allow a waveform graph? If you're looking to chart data, you're going to want to do this on your host PC. Go to Help->Find Examples and search for "Streaming DMA" You can use this to set up FIFOs to send your data to your host PC and see the data that way.
If you don't want to be dependant upon the host PC being in the system, you can bring the data to your RT, store it, and then access it later and draw it into a graph at that point. You don't want to be storing an array of data on your FPGA simply so you can view it. This is far too resource intensive.
