I know you want a 'convenient liquid' - but I would like to suggest an inconvenient alternative.
Get a supply of chemicals for Artcraft or Photographers' Formulary and then you can mix up all sorts of developers to your heart's content.
Adding P. Bromide and S. Carbonate to Dektol can affect some subtle alterations in print tone. The amount of tone change depends on the paper.
Adding Hydroquinone, Metol, S. Sulfite, Glycin and Ascorbic acid and you can make up a very wide range of paper developers: D72/Dektol, Defender 55 (?) warm-tone, Ansco 130 and the Adams' variation, Ansco 110 and 120 warm tone, Selectol/soft, Gainer's Vitamin C developers [add Phenidone to the chemical list], Gevaert 67 ultra-warm ...
Teaspoon measurements are more than adequate for paper developers, but a decent digital balance can be had for little money.