If you opened up the Downloads file (Downloads.dat) with Wordpad (need to set it to open any type), you will notice the file incomplete file locations are listed. You could potentially change them to the external drive to where the new drive is & choose the incomplete folder there.

You would then need to shift the actual incomplete files that had not earlier shifted to that location also. You could only do this whilst LW is closed. To find the Downloads.dat file you will need to access the LW preferences folder.

Example:

Change:
sq~tQC:\Documents and Settings\Administrator\My Documents\Limewire\Incomplete\T-7324901-King-Big.mp3w\xq~

To:
sq~tQF:\Drive name\Incomplete\T-7324901-King-Big.mp3w\xq~

Whatever the drive is called. Would need to be exact.