You can use almost anything to mix with the Epsom Salts . The purpose is only to mask the bitter taste of the magnesium sulfate crystals. Make sure to be well hydrated with pure water if you're not mixing the E/S with water.
The olive oil definitely much better if it is best mixed with fresh grapefruit juice. Don't juice the grapefruits too far in advance to preserve the enzymes. The live enzymes in the fresh juice mixed with the olive oil make a big difference -- there is some sort of reaction that reduces the oily residue and keeps it from being difficult to drink the olive oil.