thanks again Carlos ! 
now that’s a bunch of unintuitive steps 
I already had read those sites you posted yesterday but unfortunately didn’t “get it” that time (it was already late)
so here are the steps to do it manually [including description] since most of the time there will already be several existing partitions on the harddrive:
so to break it down:
The feature is near to be done. There were described a lot of scenarious and after diskusion with Arvin the implementation works by following steps:
create separate /boot partition (it is not encrypted)
create encrypted partition for LVM
create LVM based on encrypted partition
create logical volumes on LVM (they are not encrypted)
(#31 in https://features.opensuse.org/305633)
we’re starting at the step “Disk” of the Installation
*1) (possibility 1) if you have a completely empty harddrive and would like to go the convenient way just choose “LVM based” and check Encrypt Volume Group
afterwards click Next]
that should be enough !
e.g. for a 10 GB (virtual)harddrive the partitioning would be:
pic1
nice ! it includes /home, / (root) and a swap partition
*2) (possibility 2, based on 1)
most of the time the default partitioning isn’t good enough for your needs, either one of the partitions is too big - another one too small or there simply is one missing (e.g. /usr)
so click on Edit Partition Setup]
leave the section “Hard Disks” alone and directly go to Volume Management
the first confusing thing is that it doesn’t say that any of the partitions are encrypted (pic2) but that’s OK since the encryption was taken care of one layer up at the “Hard Disks” section (pic3) there you’ll see that there’s a padlock symbol in the “Enc” column
(total view pic4)
now to edit the LVM at the “Volume Management” section, which is called “system” you can right-click on those pre-created partitions and delete, resize or Edit
if you’re ready click on Accept to continue
*3) (possibility 3 - manual partitioning with encryption)
choose (*) “LVM based” and check [x] Encrypt Volume Group
then click on “Create Partition Setup”
afterwards choose (*) “Custom Partitioning (for experts)” (how flattering ;))
go to “Hard Disks” and add a /boot partition
“Add Partition” -> Primary Partition -> edit “Size” to 100.00 MB (or more if needed) -> “Next” -> choose the partition type to your likening at “File System” (ext2, ext3, ext4, Reiser) should be safe choices
make sure you NOT have ] ticked Encrypted device ! - you can’t boot from an encrypted /boot
at “Mount Partition” change the “Mount Point” to /boot
then click on “Finish”
those speed-concerned folks can select “No access time” at “Fstab Options”
