Got it. Here are some possible courses of action:
- get a long-scale light set (with a .095" low E) and put it on as is, untapered at the tuning post. A light gauge with a supershort scale may seem counterintuitive, but there are folks on here who can make this exact combination work, so it is an option; as for winding the E at full diameter on the post, it is a risky idea, but at <26" scale tensions are low, so it may hold just fine;*
[- drilling for string-through-body holes behind the bridge (if there's room between it and the butt of the bass) or under it may gain you a couple inches, but 2" isn't much if added to, what? ~28.5" from the ball-end anchoring to the E string post?]
- bajo sexto (Mexican octave-down 12-string guitar) strings can be had in magnetically-active winding materials (steel, nickel-plated steel, as opposed to bronze) and with ball-ends (instead of loops) from
Black Diamond - the low E reportedly tapers at 28", but is a .092", so what you gain in peace of mind (removing risk of breakage at the post) you slightly lose in tension;
[- You could take one for the team and try the Ernie Ball 2628 set (9-string Slinky guitar), and check how long the lowest .105" string is, between the ball and where it tapers;]
- get the set you want - same as you use on long-scalers, or larger to compensate for the reduced scale - and try unravelling the lowest strings (only needed for strings larger than 080, if at all - anything thinner than that is flexible enough not to break even if wound on the post untapered). Giving the string a 90-degree bend and unravelling past the bend may suffice, but then again it may not, and in that case you need to secure the rest of the string with superglue, or a short sleeve of heat-shrink tubing, between nut and post;
- this set, the Fernandes BSZ-2000 (made for their ultra-shorty Pie-Zo a.k.a. Nomad Bass, discontinued but probably still widespread in Japan, so strings for it are still being made), should be the right length already, and they're sized as BEAD strings, so tensions would be comparable to those of a normal bass:
FERNANDES BSZ-2000 Base string for PIE-ZO 4514922023598 | eBay
- Newtone Strings in Britain and Pyramid in Germany do custom sets, of whatever winding length you need.
* [EDIT to clarify: the suggested .095" would be thin enough to - hopefully - fit in the post slot without modding, and flexible enough to - also hopefully - reduce the risk of it breaking to a minimum. If the very low tension it would provide at 26" scale is not your jam, a long-scale heavy EADG (with, say, a 110 low E) or a BEAD set may work well, but in that case unravelling the lowest string(s) is a must, not only to prevent breakage, but to physically fit the string end into the post.]