Someone asked me to fill out their visa application online for the US consul because he doesn’t speak English. This is permitted however at the end it says clearly that the person applying must sign himself. It will be very difficult for the person to come down to my home to sign, is it permitted for me to sign for him relying on shelucho shel adam k’moso or is this a problem of dina d’malchusa or genevias das.
You should ask him to come and sign. Signing on behalf on the other person, if forbidden, might be a serious offence, and in this case it is not permitted both by law and by halachah.