Thanks for the tip - I'm afraid I read the spoiler
An alternative is to add these two lines at the very beginning of the "stambia.ini" file (or stambia32.ini if the OS is a 32bits system) :
Can you please tell us more about the issue you had with Java 8 ? Normally the Designer starts well with both Java 7 or 8.
By the way, make sure that you use the stambia32.exe if your java version is a 32bit version.