You will have to do this using a VBA macro.
For each cell in your worksheet, split the contents as individual items into an array, sort the array, then update the cell with the new data.
This function works
Public Sub SortACell(aCell As Range, sep As String)
Dim S1() As String
S1 = Split(aCell.Value2, sep)
Dim b As Boolean
b = QSortInPlace(S1)
Dim sorted As String
Dim s2 As Variant
For Each s2 In S1
sorted = sorted & s2 & sep
Next
sorted = Left$(sorted, Len(sorted) - 1)
aCell.Value2 = sorted
End Sub
I haven't reproduced the sorting functions here - you can find a good example at
http://www.cpearson.com/excel/SortingArrays.aspx[
^]
To call the code do something like this:
Range("A1").Select
Dim c As Range
For Each c In ActiveCell.CurrentRegion.Cells
If Trim(c.Value2) <> "" Then
SortACell c, Chr$(10)
End If
Next
Note - I've assumed that the data in your cells contains linefeeds to separate the values (because when you paste the contents they go into separate cells) - that's the
chr$(10)
as the separator