Make bootable Emergency hdd from bootable Acronis cd / ISO-Image or usb stick

Hi People,
I use different versions of acronis which all are able to built a bootable CD ROM (or .iso image file), or a bootable USB Stick to be able to boot from that CD (or usb stick) and then do some acronis tasks without a working OS.

Unfortuneately, I can't find out how to get a bootable HDD so that I finally hava an external HDD (accessed by esata or usb) which is bootable and which starts the acronis software like with a cd-rom.
There are several computers which do not have any optical device and if I had an external hdd which I can connect to an e-sata port, a recover will be done very quickly (without necessary cd-rom or usb stick). On that hdd there is more space so that I could store more acronis hdd images than on dvd or usb-stick...

Maybe there is in general a software which could convert any bootable cd-ROM/dvd-ROM/usb-stick into a bootable hdd (and vice versa?) - like it exists for bootable microsoft Windows installer images?

Many thanks for any hint!

Kind rgds Tom