There has to be a way, but I'm not really sure how this work, so hopefully there's someone else who does. But as a shortcut you can simply add a line to /etc/fstab.
Provided you are able to mount it manually, add the following to /etc/fstab:
/dev/sda1 /mnt/usb vfat rw,user,uid=500 0 0
(Note: I don't know if adding the 'auto' option would mean it will be mounted automatically when you put a memory card in, but I don't think so - I think 'auto' in fstab only means a drive will be mounted automatically on boot. Can anybody else answer this?)
Of course you have to change 'sda1', '/mnt/usb' and 'uid=500' according to your hardware configuration, desired mount point, and uid.
After that, you
a) don't need to enter the full mount command every time - simply typing mount /mnt/usb will be sufficient and
b) can mount the disk and write to it as a regular user
As for automatically mounting when you insert a memory card - as I said, I don't know, but maybe someone else does. But I hope this will at least help you to get started and use the thing :-)