Chainloading Grub4Dos
You can chainload grub4dos from grub with the linux16 command. For this you need the grub4dos exe file (grub.exe) and not the grldr file.
Here's a grub.cfg entry example:
menuentry "Chainloading Grub4dos" {
# Set root to the partition containing the grub4dos exe file
set root=(hd0,2)
# Chainload grub4dos
linux16 /grub.exe
}