Installing to CF or SD is a different matter entirely. Many computers do not recognise these cards in BIOS. If your computer does, happy day, set it is primary in BIOS and install. Away you go. But usually the BIOS is unaware of these devices and you need a kernel loaded to find them. Technically, the grub boot process includes loading a kernel to launch the real kernel. So this might work. Or it might not. It might work on one computer, but not yours.
Here's the idea:
You install Mint off of the LiveCD onto the SD/CF card as if it is a hard drive. Insert the card, boot the LiveCD, select Install, and when you get to the partitioner select MANUAL, which launches gparted. In the upper-right quadrant of the dialog, change the drive from sda to whatever your card identifies as (probably sdb). Partition, install, click on through. Now select ADVANCED for the boot manager options. You can install without a boot manager. Or you can put the boot manager somewhere else. You want the boot manager on sda. Put it there.
Now when you reboot, grub on sda will light up and try to redirect the install to sdb (where you put Mint). If it is capable of finding the SD/CF card, you're golden. If not, all hope is NOT lost.
Worst case scenario:
As above, MANUAL partitioning, but you're going to split your partitions across multiple drives as follows:
/boot - sda
/ - either
/home - sdb
Now you're GUARANTEED to have your kernel and initram on sda, the drive that is identifiable in BIOS. It loads, and it pulls everything else from the CF/SD card.