At work we had a project that required the use of a magnetic reed switch on a door that was to thin for the conventional hole mounting method. I devised this holder to allow you to mount the magnet on the face of the door and still have the switch closed when the door is closed.

This is for a switch sold as a RC36 available from many retailers for around $2-$3. The hole for the magnet is approximately 7/8"

I made three versions:

MH00- is the base magnet holder
MH-H05 has a horizontal offset of 1/2" from that of the MH00 holder
MH-V05 has a vertical offset of 1/2" from that of the MH00 holder

These files we designed in onshape

UPDATE- 8/12/2015
Here is the link to the Onshape source files:
https://cad.onshape.com/documents/9648ac2696534c6b86b0440d/w/dd639c0a49fc4babbdf6dfb1/e/591230847bb34951aa33deef

Files are sized in millimeters

UPDATE- 8/12/2015
Here is the link to the Onshape source files:
https://cad.onshape.com/documents/9648ac2696534c6b86b0440d/w/dd639c0a49fc4babbdf6dfb1/e/591230847bb34951aa33deef