Hola Shoji

That wouldn't be possible in this sentence as it would say:

He pedido un préstamo del que / del cual intereses se pagan al final.

This wouldn't be grammatically correct because you have a noun after "intereses". Cuyo, cuya, cuyos, cuyas are always followed by a  noun. With the options that you gave "del que, del cual" you are omitting the noun as they are acting as pronouns, so you can't have a noun right after. 

You could say this instead:

He pedido un préstamo del que / del cual tendré que pagar los intereses al final. 

I hope this clarified it.

Saludos

Inma