hi lola,
i feel for you. when i was an active witness...i always said "yes" before i thought about what i was being asked to do.
one thing i would never do...and everyone knew this is take the first door. i just couldn't, i had to get it together and could do the next one. some days, if i wasn't really into service...i would ask the sister if she would mind taking the next door as well. if i was lucky she wouldn't mind and we'd get lots of not-at-homes or i'd have her take most of the doors.
street witnessing isn't so bad. if you really don't want to get out of it then see how much you can get away with. don't talk to anyone if you can help it. if you do talk to someone just ask them how they're doing...comment on the weather or the landscaping, something very neutral and then wish them a great day. leave as many magazines in one place as you can. 10 on this washer, 10 on that dryer. you'll be out of literature in no time! then complain that you're real hungry and need to take a coffee break or really have to use the ladies room. sprinkle the morning with comments on how bad your menstrual cramps are today and how heavy your "flow" is. that will give you an excuse to go home early.
or...if all else fails...call up another sister in the hall that you think may be easily persuaded and tell her that you agreed to go in service with this sister but something came up. ask this sister you call if she could please, please take your place. if she says yes, call the first sister and tell her you just can't make it...but, another sister can.
if you want to fade right just start complaining to everyone that you don't feel well. you're tired and just don't have any energry. everyone will be happy to offer you advice or tell you how bad they feel. they won't question you missing so many meetings if they make up their mind you have something wrong with you.
i dunno, just my 2 cents.