"A rough cut that is created in Prelude can be opened in Premiere Pro directly."
that makes me think it has to use the prelude command > send to premiere pro. which wouldn't help in your case. but i could be reading it wrong.
so i thought, adobe was probably somewhat lazy and recycled the premiere pro project file for prelude... so i renamed the .arcutx file to a ..prproj file. and it did open just fine in premiere pro! give that a go