NXT-G is indeed very limited. There are many many things it doesn't suppot, that NXC does support.
You would need to understand I2C communications, and use the I2C read and write blocks to use it in single-shot mode with NXT-G. I don't program much at all in NXT-G, and I don't know that I could be of much help in the matter.
BTW, the Mindsensors forums are specifically for Mindsensors products. If you have questions about NXT (or any other mindstorms) in general, you should use another forum. Mindboards
has an awesome forum
(in which I am active). There are many, very knowledgeable, active people there that should be able to answer almost any questions (Software, hardware, electrical...).