I will be honest – this question is outside my expertise.

However very recent Research has shown that Chromium supplement can help diabetes.- it is used as a catlyst by the pancreas.

Retrograde ejaculation can usually only occur if bladder valve damaged. Do u know if he can ejac. with prostatic massage ? If u do not wish to do this urself u can get male sex toys (Nexus Glide etc ) that will massage prostate. This can help clear blockage ?
Otherwise u need to see urologist.