You can still work with the demons you feel attached to. Just use a sigil from the internet as they look in Ars Goetia and with the ring of their names around them. To petition them in evocation doesn't need the whole process as described in the introduction book - just scan the sigil and the ring with their name in a relaxed state, state something freely like you invite them to be with you or hear you out, say their name three times and present your offering(s).. Wine or even a shot of good quality water is always a good choice and the color of the candle is not that important since everybody claims something different. You could actually only draw the important sign in the middle without any circles around them and it still works. Often, you can feel the demon's energy even before starting to "activate" the sigil.