You might try this:
http://www.dataassist.de/en/download.shtml#tools
Look for the DA Visio User Tools. It's free.
Or if you're comfortable with VBA code, you can paste this code into Visio's
VBA editor and run it:
--------------------
Sub MakeFontSizeResizeWithShape()
Dim shpOriginal As Visio.Shape
Dim shpCopy As Visio.Shape
If Visio.ActiveWindow.Selection.Count <> 1 Then
MsgBox "No Shape selected!"
Exit Sub
End If
Set shpOriginal = Visio.ActiveWindow.Selection(1)
Set shpCopy = shpOriginal.ContainingPage.Drop(shpOriginal, _
shpOriginal.CellsU("PinX").ResultIU + 0.5, _
shpOriginal.CellsU("PinY").ResultIU + 0.5)
Dim dH As Double, dF As Double
dH = shpCopy.CellsU("Height").ResultIU
dF = shpCopy.CellsU("Char.Size").ResultIU
shpCopy.CellsU("Char.Size").FormulaForceU = dF & "*Height/" & dH
End Sub