I know exactly what you mean. I do this all the time for clients but I run an invoice for the regular ones and charge by the hour so I earn the going rate for the work. I invoice them when it becomes worthwhile but there is no contract so I am not committed to it I think they know this. I also have a minimum per incident charge for the less regular ones. It is not interesting work but I have learned that is a worthwhile revenue source. Why don't you make money from it?
Regarding the ones who call you for free consultancy (that is what it is after all), eventually you have to explain to them that your time is chargeable and that the clock is ticking when they call you. Most of them will accept this and if they don't then you don't want them as clients. ;)