New Post: drawing outside the boundaries

hi,
first, this is a really great extension!

my problem is with drawing a shape(any shape type) outside my boundaries.
i created a writablebitmap instance in the size of 20,20.
now i want to draw a rectangle from 15,0 to 35,40.
i know its out the area... , its done due to good reasons.
when trying to draw this shape i see its drawing extra lines.
any way to avoid this ?
regards.
benny.