Just to echo the "they aren't long enough" with some numbers:
My string length on my double bass (measured from bridge to nut just like an electric) is 41.5" and that's a pretty "standard" string length for 3/4-7/8 size instruments. Some double basses have string lengths around 40", some are up to 44" or longer, so it really depends on the instrument. For the most part, you're looking at something in the neighbourhood of 42".
After length: This is the distance from the bridge to the tail piece. There are a lot of schools of thought on this, some involve compensated tail pieces where there is considerably more after length for the lower strings, some involve tuning this length to a specific interval etc. Mine is 9" from bridge to the "saddle" on the tail piece, and there's probably another 1/2-1" there to get through the hole in the tail piece.
Nut-Peg: This distance is often a lot longer on double basses as well. My D peg is the farthest from the nut, and it's 8"
Peg/post: The posts on a lot of double basses are pretty wide too, often wider than big P-bass style tuners. Also, double bassists tend to wind more than the "standard" 1-3 windings around the post, with 3-6 being pretty common. That adds another 4" or so.
With all of that in mind even on a 40" scale instrument, you are looking at needing more string on a double bass than you would on an electric. Typical after-lengths on electrics don't usually exceed 3" even if it is string through, nut-peg might get up to 8-9" for 5 in line Fender style headstocks, but you're still looking at less string.
Other things to think about are wear on the fingerboard, tension, tone, if you use a bow etc. I just really can't see it working out.