The person heading for Hajj-e-Badal should perform Ifrad. It is not lawful for him to offer Tamattu. However, if the person who is sending allows him clearly to offer Tamattu then it is allowable. Hadhrat Mufti Muhammad Shafi, may Allah have mercy upon him, has detailed it in Jawahir al-Fiqh with reference.
Allah knows Best!
Darul Uloom Deoband