No, no, you don't need to export LD_LIBRARY_PATH, just start your application the way I put it
really, that's it, that specifies the environment var for that application, it will not (and should not !) appear anywhere else (as you should not interfere with the paths for other applications). No postinsts, no exports, just the above at the exact place you're starting your app.
On a side note - don't forget that Maemo has busybox and not full bash by default so a few shell things might not work as expected if you take bash for granted.