PDFLRF does an excellent job formatting the text for a small screen. The biggest problems are (1) the LRF output format, though that shouldn't be a problem if you're using a Sony, and (2) it rasterizes everything, so the file is much larger, and you can't use dictionary/search functions (not really a problem on the 505).
If you are mainly attracted to sopdf for its autocropping features, there are ways of using ghostscript and calibre together to autocrop a PDF.
Details here. That doesn't split each page into subpages the way soPdf and PDFLRF do, but putting the reader in landscape mode achieves pretty much the same thing. (I just hate how the Sony grays out the boundary between the two halves in landscape mode...)