I use AutoIT to handle this situation.
It's a free programming language that can look at window titles and react based on them, such as (not exact, but close enough to give the idea)
while(1) ; forever
$size_creo = WinGetPos("Creo Active")
$size_excel = WingetPos("Excel")
IF WinActive("Creo Active") and $size[2] <> right_width and $size[0] <> left_edge then
WinMove("Creo Active", new size, loc)
WinMove("Excel", new size, loc)
EndIf
wend
Leave this running when you want the split screen and stop it when you don't.