I don't like depending on insufficient agitation and developer exhaustion to control contrast; it's way too inconsistent and results in what's probably not wanted, reduced highlight contrast to the point of blocking.(posted 8988 days ago)Much better imho to try to keep the curve shape straight and use a shorter development time to accomodate the high SBR.
But if you must: Rodinal 1:75 to 1:200, changing the agitation cycle to 10 seconds every minute rather than 5 seconds every 30 seconds. Beware that unevenness, streaks and sprocket-hole streamers are likely. Also add about 10g/liter sodium sulfite to help keep the EI up with such a weak solution; no point in ending up with an EI 6 film.
Alternatives that put a strong shoulder in film are split developers and FG-7/TG-7.
It might be easier to simply burn in the excessive highlights using a #0 filter.