How to boot FreeBSD and linux from FreeBSD MBR?

[Yuri]

When I installed ubuntu on another partition, it overwrote BSD MBR with 
grub one.
Now grub boots ubuntu without even asking what to boot.
When I tried to restore BSD MBR, BSD boots but linux doesn't. This is 
because there is no bootable PBR in linux partition.
When I tried to install grub into PBR on its own partition, like someone 
online suggested, it refused with the message that this is dangerous, etc.

So is there a way to boot both linux and BSD from BSD MBR (by pressing 
F2 or whatever)?
Are there quick instructions anywhere?
I just don't want grub to take over the boot process.

Yuri