I can think of a couple of ways that you may be able to perform this type of operation. First, you could use a digital pattern generation, and regenerate that pattern. You would have to have a faster sample clock, so that each pulse would be more than one sample on the digital line. (For example, perhaps your complete pattern could be 20 samples: 7 high, 3 low, 2 high, 8 low, and then that would repeat.)
The other way to perform this would be using the buffered counter output functionality on X-series devices. This allows you to pass a buffer of counter samples, with each sample consisting of a frequency and duty cycle. If you use implicit timing, then it will output one cycle of each before moving to the next sample in the list.
-Christina
