XoloX already builds the 'end'file as it downlaods. Segment#-1.xlx is always the beginning of the file you are downloading, and it's added to, like all the oher segments, whenever an adjoining segment is completed or cut off.

Viewing the files in /temp while downloading is not possible, and even while not currently active not advisable, as they would be locked and unable to be appended. You can copy a segment and try opening it by changing the extension or dragging it into an application, but it will be somewhere in the middle if it's not the first segment, and some file types need the header at the beggining to be viewed (AVI, ASF, etc) so even if you're 98% done with the file, you can only really see however much of that is in the first segment. (AVI files also must be fixed, as the header information will conflict with the file size and you will get an error)