Mixing with other liquids only increases the volume you will have to drink in a short period of time, with little guarantee of masking the taste adequately. 2 bottles is nearly a cup of liquid itself. It also means raising the risk of vomiting; your antiemetics should still work.... but that's not entirely reassuring, is it?
A user here with a medical/science background also explained that adding acidity (like juice or honey) to N will alter its pH. N is apparently made from an acid with an alkyl group, which is needed for it to have its CNS effects. Adding acidity means altering this chemical property needed for its action; also not a risk you can afford. Some people recommend adding sugar to the mixture (which has a high pH) but it's unclear if it will dissolve.
I don't believe the taste is quite as bad as people make it seem. Remember the concentration of the powder used at Dignitas is stronger and therefore should taste worse than liquid N. These patients follow the drink with chocolate, which seems to work just fine.