As I understand it pure DXM does not have a great oral bioavailability when taken orally because it has solubility issues. This may be solved with alcohols or DMSO, the former is not really recommended to ingest in serious quantities with DXM since it tends to produce dizziness, nausea etc but a small bit to take it should be okay.. and DMSO is of course pretty unusual and it tastes weird even if you get it past your tongue.
I don't know if this is as common an issue as I think it is - if so it should be all over the dextroverse forum, so check - but it is the reaction I got back from DXM users looking into the pure stuff as a solution (no pun intended).
If I were you actually I would try to find out if it dissolves in something like PG / PEG and go from there...