Did you try making the bottom a welded flat and attach the lugs to the shell? You will undoubtedly fail the bottom but it may work. Is the tank/vessel mechanically or self-anchored?
Why don't you simply write a spreadsheet or do hand calculations? I strongly dislike the type of work around I wrote above; it seems like forcing the program to do something it isn't necessarily meant to do. Why don't you use the building code requirements which will likely direct you to an API 650 or similar methodology (depending on where you are)?
Compress, PVElite, etc. are great for getting you most of the way there and sometimes other means are needed to finalize or at least verify the result. Also, for the attachment (if you are using ASCE 7) see if you need to include the over strength factor Ω; the last time I checked Compress didn't included it. Normally I design the lugs/chairs/etc. outside of Compress so i don't typically look in the support calculations.
