i've found that it's possible to revert the logical volume to a standard partition without losing content!
After yosemite installation, when you reboot using unibeast key, open a terminal.
Type: Diskutil list
you will find the logical volume uuid, in my case, 426118d9-ea6a-49ab-b92f-686df1f9b325
$ diskutil list
/dev/disk0
#: Type name size identifier
0: Guid_partition_scheme *128.0 gb disk0
1: Efi efi 209.7 mb disk0s1
2: Apple_corestorage 127.2 gb disk0s2
3: Apple_boot recovery hd 650.0 mb disk0s3
/dev/disk1
#: Type name size identifier
0: Apple_hfs yosemite ssd *126.8 gb disk1
logical volume on disk0s2
426118d9-ea6a-49ab-b92f-686df1f9b325
unencrypted
use the following command to "revert" the logical volume to a standard partition and also remove core storage:
Diskutil cs revert 426118d9-ea6a-49ab-b92f-686df1f9b325
the command take only a few seconds, then you have to reboot.
You will now have the following:
Diskutil list
/dev/disk0
#: Type name size identifier
0: Guid_partition_scheme *128.0 gb disk0
1: Efi efi 209.7 mb disk0s1
2: Apple_hfs yosemite ssd 127.2 gb disk0s2
3: Apple_boot recovery hd 650.0 mb disk0s3
multibeast and clover will be able to install their boot loader as it should normally!