Below is an image of the Evolution Gun Works bag rider that was designed to level the toe of A2 stocks. It may not be the exact "fix" you're looking for, but may give you some ideas. If you do a search for "rear bag rider", you will pull up quite a few images that might be of help in terms of ideas if you plan to design your own.
FWIW - I shoot F-TR and started early on with rifles having McMillan A5 stocks, which also have a steeply angled toe. Because I really favor the feel of the A5 stock, I am unwilling to change, and I also am not a huge fan of the idea of having to re-stock multiple F-TR rifles with expensive stocks. Fortunately, due to my my shooting style, which consists of preloading an LRA bipod (which is basically a grossly over-sized Harris/Atlas-style bipod), and a large rear bean bag, the angled toe is not an issue. However, I may be the last dinosaur on the planet still using such a setup in F-TR. It works for me, but most F-TR shooters have gravitated toward a ski-type bipod and an eared rear bag. Commonly referred to as shooting "free recoil", it is a very different style of shooting than what I use, and having a steeply angle toe means the muzzle will be pointing 30 feet above the target at the end of the recoil impulse. I also have such a bipod and have played around with this shooting style from time to time, hence my prior interest in bag riders. Over time, I simply decided to stick with what has worked for me in the past (i.e. preloaded bipod, rear bean bag).
Given that the bullet dwell time in the barrel is more than twice as long with the slower rimfire cartridge than most centerfire cartridges, the forgiveness for shooter gun handling errors is even less when shooting rimfire. You may get away with using a stock that has an angled toe, or you may find that designing some kind of bag rider will work well enough for the time being. However, I would suggest that best time to consider purchasing a stock with a toe that is more appropriate for the type of shooting you intend is now, while you only have the one rifle to worry about. It may be more painful ($$$) in the short term, but in the long term you will likely be better off getting a stock that is purpose-built for BR shooting. In doing so, you can also choose an eared rear bag that is perfectly mated to the stock toe of your choice, and end up with a setup that should never be the limiting factor in your shooting. This is just my opinion, but having been down the same road, I suspect I might have been better off in the long by switching to a more appropriate style of stock for F-TR shooting. Had I done so, that style of shooting would have long since become my "new normal".