custom date format question

I am trying to come up with an elegant way to format dates for
the following scenario:

month and year are always the same in a given worksheet. For
example March(03) and 2005(05). The column cells are formatted
as mm/dd/yy using format and cells, selecting date and choosing
the 01/14/01 format entry.

What I want to do is simply to enter the day of the month (for
example "11") and have it be formatted as 03/11/05. Seems
like there has to be a best way to do this. If all you have done
is set the format for mm/dd/yy then entering "11" results in
03/11/00 (where the 00 is the default 1900 date for year).
Then you can highlite the cells, select "Edit" followed by
"Replace All" using (from=1900) and (to=2005). That works
but is an offensive method of handling this type of format and
fill operation.

Is there a better way perhaps through using a =DATE() call
or something that can be pre-programmed into the worksheet
to make this automatic? I don't want to write a macro if it can
be avoided, ditto with VB macros.

Please explain your solution in detail. Thanx.

You could have pre set values but it will only be for "show": "05/"#"/05"
Otherwise it has to be some kind of programming.
Ola Sandström