Well, just play the notes on the E string 2 frets down (towards the nut) and you will be playing the same notes ? Although it sounds better in Drop D, why cant you play it in drop d, its easy enough to tune it back E.
I play it on a 5er so for the dropped notes I just move down a string. Are you transcribing it or just wanting to know what to do with the low D? You could just bump the D up an octave (A string for example). If you're reading if off of tab, subtract 2 from the numbers on the lowest string. So if it says 4, you play it on 2 on the E. Like in this tab: http://www.bassmasta.net/a/adams,_bryan/101574.html Wherever is says 0 for open D, just play the D somewhere else (easiest on the A string). Won't quite have the growl of being in drop D, but may blend better.
Errrrrrrrrrrrrrrr ......... On the A string, go to the 5th fret. That's a D. For the A in the next part of the verse you can play the string open or drop your finger down one string and stay on the 5th fret (5th fret on E is an A) Might wanna grab yourself a fretboard chart if your band is going to do a lot of songs in drop D and you aren't tuning that way