No, because then you would violate the duty cycle regulations for the frequencies used.
What you could do, is create messages less often (so you will be certain that the frequencies are “free” again when you do, see Spreadsheet for LoRa airtime calculation for a tool to calculate this), or you could detect the case where your message is waiting for airtime and sleep in the mean time. Doing the latter might be tricky with the current LMIC code, since the next available tx time is not easily exposed. Look at the engineUpdate function in lmic.c to see what happens when the library decides to wait for airtime.