Unfortunately all Part 147 schools I know of are Fulltime and unfortunately you cannot miss anytime without making it up. Plus if you miss too much time you may not graduate at all.
Like Inewby said, if you find a shop that will allow you to work with them you can earn either your powerplant or airframe in 18 months. If you want both(which you will probably need) it will take at least 30 months. All of this can be found in FAR 65 subpart D. Here is the link on the FAA website:
http://ecfr.gpoaccess.gov/cgi/t/text....0.1.1.4.4.1.4
The good news is if you ever become unemployed, most state unemployment benefits will pay for your schooling. So if you are unable to do it now you would be able to do it then. There were several guys in my school that went through that way.
If you do find a shop in your area that is willing to do this please let me know as I like to help people in get into the aviation maintenance field.
If you want more information or advice please feel free to PM me.