WARNING and Disclaimer: I`m not responsible for any damages done to either your Raspberry or to your SD card. - Take a backup!
I just sat and fiddled around with an old SD card that has been used for my very old Raspberry Pi B v1.
Both the raspberry and the card have for separate reasons stopped working.
I took the SD card apart and realised that the actual memory only stored on the front end of the card.
Therefore taking a sturdy cutter and cut it apart... as crazy as it sounds should work very well with your raspberry.
The cut should be made 2 mm after the R/W switch towards the back of the card so you wont hit the sturdy plastic structure of the card. The card should be intact and working after the procedure.
No need to have an extending SD card any more!
Pictures of SD coming if someone is interested?
The SD card is a SanDisk Ultra SDHC 1 Class10 30MB/s
I hope this will help someone out there.
Full disclosure: I did this on a broken SD card and have never tried it on a running machine.