Strange, I needed the same thing yesterday.
I used the code below in the "right click event". I could drag over the range with the LMB. Right click combines to first cell in range and clears the rest.
It delimits the merged text with a semi-colon and a space.
Hope it helps.
Private Sub Workbook_SheetBeforeRightClick(ByVal Sh As Object, ByVal Target As Range, Cancel As Boolean)
Dim oRange As Range
Dim oCell As Range
Dim sTemp As String
Set oRange = Application.Selection
sTemp = ""
For Each oCell In oRange
If oCell.Value <> "" Then
sTemp = sTemp & oCell.Value & "; "
sTemp = Left(sTemp, (Len(sTemp) - 2))
oRange.Cells(1).Value = sTemp