I have managed to find a solution to the problem. It seems that you can send Ctrl+F9 to get a 1/8, Ctrl+F10 for 1/32 and Ctrl+F11 for 1/64.
so to send 4.125 you should sendkeys.send("4 ^{F9}") = 4 1/8 or for 4.625 you should sendkeys.send("4 5^{F9}") = 4 5/8
Hope this helps someone else.