tkamiya. The drum option might be your best bet.
Richard Henry did fairly extensive densitometric testing of Dektol at various dilutions, development times with factorial development etc. At dilutions greater than 1+2 dmax began to fall off even with increased development time and there was increasing compression of all densities > approx 1.5. Further, development times greater than 8 minutes tended to cause fogging problems. Granted, these tests were with Ilfobrom in the 80s, but still probably directionally useful.