i helped linda with the DK tobacco base ingredients. it's spot on and I'll be buying a big bottle too when it's available. it will mix well with anything.
play with cheesecake, plum, chocolate, maple, dk tobacco base, caramel, EM or marshmallow for a Ry4'ish sweetness. Not quite there, but pretty close. If you have graham cracker, add that too, or in place of some of the previous ones if you don't have them.
go EASY on the plum. I play around with about 4mls in a bottle with pg only and start adding drops of each until i get the flavor right.
go easy on the cheesecake too, because after a day, that flavor will overpower the juice.
a drop at a time, smell and tweak. go easy on the DK tobacco base too. it tastes stronger than it smells. when she sent me the sample, i called her immediately and did a holy crap, yep that's IT
the Cola is strong too. a little goes a long way unless you like a massive TH

after a day of sitting i get a whiff of cinnamon from the cola juice mixed. maybe that's coke's secret ingredient?