Using constant instead of serial.read()

I have not used those wireless modules but this seems straightforward

radio.send(TONODEID, sendbuffer, sendlength);

and sends the first sendlength bytes from the array sendbuffer

To send a fixed message try this

char myTestMessage[] = "Hello World";
radio.send(TONODEID, myTestMessage, sizeof(myTestMessage));

...R

Edit to add [] - hope it's correct now