Most of the forum links will have no index tags and they won't index in Google. So, make sure of that and proceed further on indexing them.
you're most probably referring to nofollow, most of forum links are indexable,
OP, i'm not dealing with any of these fasting methods, neither having any noticable experience with it,
as far as i know, one of the methods used by some of the big players would be to buy a bunch of authority news/jobs websites & use them,
that incudes both 301s/cloacking & links in the posts,
i've tried the same with a bunch of new domains around a couple of years back, worked well for crawling & indexing in less than an hour,
the method got patched afterwards, but it seems like it still working with any domain/website that got decent authority,
especially with multiple of them, the work will be more guaranteed,
make your own research,
i didn't test or have any experience with these,
but there's solid cash to be made with the CPA, streaming & live sports websites with these