Hello,
There are some solutions to what you want to do. The first one is to read from the spread sheet and write directly to the RT VI, using the VI Server VIs. You need to open an Application Reference where you will specify the address of the RT box, then an open VI reference that will make reference to the VI running on the RT. And then through methods and properties you can write the values to it. Another option is to use the Call By Reference instead of the properties and methods.
The other solution is to write and read data from the RT to the Host or vice versa by using TCP communication.
If you run your RT VI through the Communication Wizard, it will create 3 different VIs. One with the TCL that will be running at time critical loop your VI. Then a NPL which will be a VI with normal priority for communication. This is where you will have the TCP communication. The third VI will be a Host VI that will also have the User Interface and the TCP communication to the RT.
Hope this helps.
Ricardo