Fyo-

Dont overthink this.... You will get to repack this yourself, correct?

When asked about 'did anyone give you anything to carry' just response "my friend and I are traveling together and I have some of his stuff, but I did re-pack everything myself". Casual, not worried. Worst case they flag that bag for an intensive screening.

I would have zero concerns with 'fraud' or the airline- nothing says that your bags must consist of luggage and clothing owned by you personally.