First, what platform will you use for the grid. If non-windows, I hardly think this will work at all.
Secondly, using DDE doesn't sound like a typically grid application, so either, you might want to find a path in you solution to execute jobs "on the side" of the grid, in a more traditional manner.
I'm no expert in Excel tagsets, but is it critical for you ta have native Excel files?
There are, as might know, alternatives that could be considered, such as loading via Libname Excel engine, or accessing reports via Add-in for MS Office which let's you do some extensive formatting of your Excel report.
Data never sleeps