M.A.S.H. - 2016-12-04

I run debian jessie on HP Probook 6475b. I can install and start rEFInd and boot from internal laptop HDD.
Due to my setup I would like to boot system from SD card but rEFInd does not find it.
I think my problem is similar to that desribed here: https://sourceforge.net/p/refind/discussion/general/thread/f6e24cea/
but on HP laptop there is no way to start EFI firmware using some kind of "option" key (or I did not find such a way).

What I already tried:
- starting refind from internal HDD and external USB works;
- finding .efi files and booting from HDD and external USB works;
- finding and booting from SD card does not work.

What is interensting, when I start EFI shell I can confirm that SD card is found and listed as a block device (blkx:). However it is not mounted as a filesystem (fsx:).
Is there a way to map or mount block device as a filesystem?