Hi there,
one way...
do you have an external drive the same size or larger than your internal one ?
If so use
Carbon Copy Cloner to 'clone' Internal drive to the external, then boot from the external, format the internal drive and 'clone' the external back to the internal.
You now have a nice backup and a contiguous internal drive.
If you have TechToolPro you can also defrag in that, but you have to boot from a different disk...that the one you want to defrag...
regards
Ric