I think I can also safely eliminate Up, Id, Eh, Uh, Um, Yo, Ex, Ow, and Ox.
More words I think I’ve exploited to their utmost : Op, Ho, No, Oh, Hi, Or, On, Ma.
So far, leaving out “song words” like Re, La, Ti… 
Only the following have remaining promise, of those I’ve looked at : We, My, By, Ad, As, He, At, Am, Pa, Go.