While I was posting, I went ahead and googled your bass. If I've read correctly the scale is 27", so I expected more or less 28" as the minimum winding length requirement.
In light of this, I propose an experiment. Your money, of course, so just give it a thought and see if you're up for it:
even though they said they don't make anyting suitable (a company will often understandably err on the side of caution), La Bella makes a flatwound set for the Gold Tone Mbass, named MBLS (aka MBSLS on the eBay):
MBLS MicroBass LaBella Flat Wound Strings
They are,
reportedly, 28" long from ball to heastock-side silk. In other words, if you peel of the silk, and keep the string lifted from the nut slots (with a pencil under them ahead of the nut, or equivalent) while they stretch - which they do, up to a fraction of an inch - they might just fit.
In your shoes I'd give them a try, and if they don't work I'd cut my losses and resell them.
Alternatively, you could go the custom route and contact
Pyramid Strings of Germany (an email will suffice, but they'll also ask for precise measurements). They also make flats, and also black nylon tapewounds.