Yes, it is possible. There are linux defraggers available. However, because of the excellent design of linux file systems, defragmentation is not necessary on a linux box. Some of the defraggers will even warn you not to use them. You can easily scramble inodes that way.
However, if you're dual booting Windows and Linux, then use the Windows defragger on the Windows partition, it will need it.
Iolair MacWalter