Detaching several Direct LUNs from a VM is supported in 3.5.0 (and probably in 3.4 too, I admit I did not bisect when exactly this was added).
From the Disks subtab under the VMs maintab:
1. Select multiple disks using the CTRL button
2. Click Remove (or right click->remove)
3. DO NOT CHECK THE "Remove Permanently" CHECKBOX!!!
4. Click OK to confirm