The Elinchrom Octa bank has a built-in stand adaptor that supports the weight of the bank and head. The stand adaptor includes a handle for control and also provides the attachment points for the internal die-cast metal bracket that positions the head in the optical center of the bank. Finally, the bank itself is engineered to fold like an umbrella.
Assuming you just want to turn your head around, there are a couple of issues you have to overcome. The Chimera Octaplus uses a speed ring, which means there's a hole in the back of the modifier that you would have to close. Then there's the head bracket itself. You might start by modifiying the Chimera stand adaptor and grip head that are made for the Octaplus. If you (or a friend) are handy with metalwork and fabrication, you can probably make a bracket for the inside of the Octaplus to which you can attach your strobe.
For what it's worth, the internal baffle supplied with the Octaplus is graduated so as to keep the light spread even from center to edge (less than 1/3 stop falloff). This assumes you use the modifier as intended. I don't know how much time you want to spend designing and adjusting a custom bracket to turn the head around, but you might have a hard time getting the light to spread as evenly as it does by default.
I'm not sure what you mean by "absurd amount of money". The difference in price between the two banks, new and ready to use, is less than $150. That includes the price of an Elinchrom-made adapter that allows you to mount other manufacturer's heads in the Octa bank. Unless you bought the Chimera unit used, you aren't saving much money. And if you consider the cost of time and materials to design, construct, and fit your custom bracket you will in all likelyhood end up spending more.
People who do stupid things with dangerous substances often die! -me