You can do this manually by entering numbers interspersed with operator symbols (Insert > Symbol), and then edit the character string to apply the Symbol font to the operator symbol characters. That's a nuisance.

You could not use a form just to insert the symbols as you typed into a cell, because when Excel is in Edit mode, it doesn't listen to anything else.

I think you would need to use a form that has buttons (for both numbers and operators) that builds an expression string in a text box, and then moves it to the worksheet.