One of the simple ways I've created low contrast developers (for microfilm) in the past was simply reducing the level of developing agent.
Ordinary dilution isn't likely the best way to go here, though it can work (I've processed microfilm in Parodinal by using 1:100 dilution and reduced agitation and got very acceptable results, though the speed was nothing to write home about). Dilution with a solution similar to the developer, but without developing agent(s) can produce less of change in grain character than dilution with plain water. The SDS should tell you whether the developer uses carbonate (likely), borax, etc. for its alkali, and for a European product may actually give a hint how much sulfite is in it -- so you'd just make up a solution of sulfite and the appropriate alkali and cut the developer about 1+3 with this solution before diluting for actual processing.
Or you could use the contrast developer you have to develop prints -- it's probably similar to Dektol anyway...