I just wanted to do the exact same thing (writing a recovery disk to an image file instead of a physical DVD), and looked for a software, and I found one for free which did the job without a problem:
BTW I have no connection to the company, but I highly recommend this software, because it was very easy to use and did the job.
Here's a short description which I found first:
To use TotalMounter as a virtual burner, mount a virtual CD/DVD RW
from the Mount menu. Select whether you want to burn a CD image or a
DVD image, where the file will be stored and give it a name. Now, the
virtual drive is ready as a CD/DVD RW drive. You can then select this
drive as the destination drive from your usual burning software and
write to it. The data will be saved in an ISO image file.
After installing, you have to wait until the "KernSafe SCSI Controller" driver really gets installed (otherwise you can not mount a new device; BTW I covered installing other drivers on the picture which do not belong to this software):
After running TotalMounter, you have to select Mount > Virtual CD/DVD RW:
In the "Mount Device" window, select DVD, type in an appropriate size:
Device gets mounted:
Select the appropriate device in the recovery management software:
And the writing process was successful for me:
After the writing process, I simply clicked on the device in TotalMounter and unmounted it (there's an Unmount button). (The final result was an iso file with a size of 8.87 GB.)