Offer dofollow link from a paid option

Hi, for SEO and registrants wishing their SEO work on my directory, register on a directory has no purpose if the link to their site is not nofollow (blocked Google bot). I think many more people would fit in my directory if the link to their site was dofollow. Is it possible to do this with your theme ? or would it possible to make it possible from a paid option ?
I think it is important an important option for a directory.