Pilot based interpolation

Hi all,

i'd like to ask about pilot based interpolation in channel estimation
of OFDM cells. I have a block of reference cells which i need to
interpolate in time and frequency domain. An example :

xo....................oxooxooxooxooxooo
oo....................ooxoooxooooxoooox
ox....................ooxoooxoooxoooxoo
xo....................ooooxoooxooooxooo
oo....................oxooooxoooxoooooo <----corner

How do i interpolate a reference cell at the border? I know u can
implement interpolation in both time and frequency directions but i
have no idea how to interpolate reference cells a corner/border without
the help of pilot cells. Can i use nearest neighbour interpolation? Or
is there a smarter way? Thanx in advance for all ur time!