I tried it and was successful. The boot commands you can see in the menu.lst file created by the multiboot installer are different for different linux oses and also for windows type boot cds. eg : look for ultimate boot cd commands and other linux oses.
According to what I know, may be wrong, avast bart cd boots similar to windows cds. Idk. But I have assumed. Because it is based on win pe environment.
I had the windows 7 rescue disk : which you can find on bob's software list.
I just did this:
1. format the usb to fat32.
2. copy windows rescue disk to usb.
3. renamed it to winrd.iso (there should be no spaces in the name of the file- to be safe.)
4. opened MultiBootISOs-v1.4.5.exe by pendrive linux and followed the instructions, I mean i selected my pen drive and it copied a few files.
Now is the harder one, or rather easier one.
6. opened the menu.lst file using notepad++ and entered the following code at the end of the file :
title windows rescue disk
find --set-root /winrd.iso
map /winrd.iso (hd32)
note : the file windows rescue disk was renamed to winrd.iso and it should be in the pendirve. I mean, if your pen dirve is h: , the file should be in h:\ not inside other folder.
lmk what happened.
EDIT : But as I can see, you have already tried this stuff, So without bart cd iso, I can't help. But let me try, what error do you get?