At this point it looks like you're pretty determined to have coke with *something* but I think MDMA may not be what you're looking for. In terms of perceived short-term effects only: It's been many people's experience (as I've read in the past here, and elsewhere) that cocaine can practically nullify the MDMA high, to the point that someone can be peaking as hard as you like, and then rail up a fat gagger of coke and be "straight as a judge" within minutes.
Obviously this is not *really* becoming sober, but something about the conflicting neurotransmitter effects of both drugs really plays havoc with the MDMA peak. I'm pretty sure this isn't a chance occurrence due to the number of people who've expressed their opinion to me in the past that "coke kills a pill". Personally I'd wait until the pill is over before having the coke, or have it well in advance, otherwise you may feel that you've wasted your money on the pill.
Some people do feel that you can have a line of coke and it will utterly replace the MDMA high for the duration of the coke buzz, and then the MDMA 'comes back' after the coke wears off. However, I think that if you're only taking a single pill, the peak is likely to be 1-2hrs long at best, and decent coke should last up to an hour or even an hour and a half before it's completely worn off... so you can do the maths there.
Whether this combination is unsafe in terms of neurotoxicity is another issue altogether... but given the nullifying effects of combining the two, you probably won't want to do that anyway.
BigTrancer