Wanting to do that is completely idiotic, because going fractional on Bitcoin does not amount to the same thing as it would with fiat deposits.

The advantage to going fractional on fiat deposits is to maximize profits through leverage, predicated on the assumption that the risk/return on lending out fiat deposits works in the depository's favor on average.

With Bitcoin, that's the most insane and dangerous proposition ever, because it isn't exactly rocket science to see from past performance that becoming illiquid in Bitcoin can result in a situation where after a large rally, the operator would never ever be able to buy back adequate reserves, because the returns in Bitcoin itself were higher than anything they could've ever done through leverage. This could only ever happen in a situation where you had a robust Bitcoin credit economy where returns themselves were denominated in Bitcoin directly.

Basically there is no way to do this without actually being a straight Ponzi. Trying to operate a plan like this amounts to massively shorting Bitcoin at all times (without customer consent) risking shorting into an enormous rally that ends you.