Installing a custom recovery on ASUS MemoPad 7 (ME572C)?

Hello,
I'm running a rooted Lollipop 5.0.1 ("LRX22C.WW_epad-V12.14.1.17_20150713 044030454_201502120108") on my ASUS MemoPad 7 (ME572C) (WiFi + LTE) and I'd like to install the "Xpose for Lollipop" framework to it.
Therefore I downloaded the necessary files ("XposedInstaller_3.0_alpha4.apk" and "xposed-v72-sdk-x86.zip"). Installation of the apk was no problem, but I ran into problems when trying to install the zip. It seems that I only can install it via a custom recovery like CWM or TWRP. And to install one of this it's presupposed to have an unlocked bootloader. But I learned that it is currently impossible to unlock the bootloader officialy.
So I tried the following to install the zip without having a custom recovery:

• tried the apps "Flashify (for root users)" and "[ROOT] Rashr - Flash Tool" without success. Flashify reports to have installed the zip but when I opened a file browser to check if the files were copied into the system folder or its subfolders they were not copied. And Rashr just installs zips when a custom recovery is installed

• tried to copy the zip contents manually to the system folder and its subfolders with my "TotalCommander" file browser without success because writing access to that folder were denied

• tried to copy the zip contents manually to the system folder and its subfolders with the root file browser of my "ROM Toolbox Pro". I was able to copy the files, but after restart it seems that the Memo Pad is stuck in a boot loop AFTER displaying the INTEL logo

Now I'm of the opinion, that I need to install a custom recovery. But how do I do that without unlocking the bootloader? There must be a way because I saw articles in the internet saying that they have flashed such a recovery but don't telling how.
Is there someone who can tell me how I do that?