triple boot using win7, wubi14.04, wubi16.04

I have been using Wubi 14.04 since many years to my complete satisfaction alongside with Win7. I now want to move to Wubi 16.04 and install it as a triple boot with EasyBCD for testing purposes. However, I found no way to direct the boot loader to use a wubildr.mbr NOT located in C:\. The wubildr.mbr corresponding to ubuntu-14.04 is sitting in C:\ and it is found but when I want to use C:\ubuntu_16.04\winboot\wubildr.mbr (and give this path in bcdedit for booting the new installation it is simply not being found. Is there any solution?
Thanks a lot, best, D-E