First thing that comes to mind is formaldehyde (imine formation) followed by reduction (NaBH4).
Problem with this is that I don't think methylene imines are stable enough to be isolated (I could be wrong). You can do reductive amination with formaldehyde and a reducing agent (e.g. H2
/Pd, Zn/AcOH, HCOOH etc.) but primary amines dimethylate.
I don't have time to check right now, but this problem must have been addressed in the literature. Off the top of my head, you could perhaps peracetylate, alkylate the resulting amide, then strip off all the acetates (Zemplen conditions will de-acetylate esters and tertiary amides). Not pretty, but I reckon it's pretty safe.