How big is the USB drive?
dd if=TinyCore-6.1.iso of=/dev/sdx
where sdx is your usb drive. However, the bigger your usb drive the bigger the waste.
Another way is to make the usb drive bootable, install grub2 on it, copy the ISO file to the usb drive, get the label (or UUID) from the usb drive and edit grub.cfg:
menuentry "TinyCore 6.1" {
set isofile=/TinyCore-6.1.iso
loopback loop $isofile
echo Loading vmlinuz ...
linux (loop)/boot/vmlinuz -- iso=LABEL="your label"$isofile cde
echo Loading core.gz ...
initrd (loop)/boot/core.gz
}