There is a way to update to 9.2 without a game. You have to update emunand to 9.2 using CIAs built with UpdateCDN or 3DNUS, then use rxTools to flash a firm0/firm1 bin files from a working 9.2 dump. Since you don't have 9.2, you'd have to obtain these files from someone else. I have successfully updated my 4.5 3DS XL to 9.2 using just CIAs built using UpdateCDN. (used 3DNUS to build eShop CIA as the one from UpdateCDN wouldn't install). Then injected the firm0.bin/firm1.bin files to emunand using rxTools. (files must be named emu_firm0.bin and emu_firm1.bin and you need to have version 1.3 or higher as rxTools 1.2 and older did not feature emunand injection yet)
The emu_firm0/emu_firm1.bin files should be located in a folder called "nand" at the root of your SD card. That's where rxTools expects them to be when injecting partition dumps back into emunand. rxTools doesn't yet support injecting directly to sysnand. But even if it did, it would not work in this case as you wouldn't be able to boot into rxTools after updating system to 9.2 (as then you'd have to install the CIAs directly to sysnand. But that's a very bad idea as I have just mentioned). The system will likely lockup if you try to use anything after updating to 9.2 directly. (normally the 3DS reboots, but DevMan doesn't force you to do that)
Either way, you must use emunand to update to 9.2, then inject working firm files from an existing 9.2 dump, then extract that emunand and flash it to sysnand using Gateway menu.
That's pretty much how I did it. I did notice the friends list menu locked up the first time I tried to use it after updating to 9.2. I formatted from system settings and it worked fine after that. So certain settings you had on 4.x may not update correctly once on 9.2. If you notice certain things locking up like the friends list, you'll need to format the system to reset it so that it works.