I wonder if you could add Sifo Dyas to TPM by tweaking sidious’ holograms and keep only his scene with Maul on coruscant as a cameo.
The tricky thing might be to write and record Sifo Dyas new dialogue so that it is evident that he is merely the messenger and not the real mastermind.
Other than that there could be some opportunities to hint at his real identity, for example it could be him that warns Gunray that the ambassadors are Jedi knights or he could propose to buy a better army.
Cough, cough, clones or something, cough, cough.