W-w-w-w-ait (that's a stutter). You're going to do what to do what?
Okay, you said you are going to use Cream of Wheat as a filler to keep the bullet from sinking into the case. This isn't the solution if I am reading this problem correctly. You should have adequate bullet pull (tension) on a loaded cartridge to prevent the problem of the bullet being driven into the case. In other words, the tightness of the brass around a seated bullet should hold it in place.
.44-40 (or .44 WCF) can be a problematic cartridge to load. The brass case is very thin and it can be difficult to get adequate bullet pull. It's very important to have a sizer plug in your flaring (#2 die) die. Often when the (presumably) properly sized case is cycled through the flaring die, the sizing plug opens it up too large. This causes you to not get proper tension when the bullet is seated. RCBS (and some other brands) dies use a true sizing plug; Lee dies do not, they flare without providing exact case sizing and in this matter, that might be a good thing for you.
Another thing is, .44-40 should have a firm roll crimp on a seated bullet. If you are using lead bullets designed without a crimping groove, use a different design.
Another technique that I've seen people use to secure their bullets on this caliber is the use of a Lee "factory crimp die" which literally crushes the case into the bullet shank with a hefty crimp. I prefer to get the sizes of components and dies right and make it work properly. As I said, these cases are thin and fragile and the "factory crimp" is hard on brass. At a minimum, you will be trimming these more often from using such a crimp and I've seen where the "factory crimp collet edge actually cuts through the thin .44-40 case mouth.
Once in a while, you might encounter a sizing (#1) die in a set that won't size .44-40 down enough.
You didn't say what brand dies were being used. Here's an approach you might take. Send the die set back to the manufacturer, supply them with samples of the components you are using including a dummy (uncharged cartridge, no primer or powder but with bullet seated as you normally would attempt it), and a letter of explanation as to what the problem is. They can then look at this as a system and determine what the trouble is.
I wouldn't use a filler for the problem that you describe. That would be an unacceptable work-around. It might have it's own consequences. People have used fillers (like Cream of Wheat) before to enhance ingition of powders in large volume cases and even at that, problems come up. You did not say what your load of Unique was, but you said you would reduce it for the rifle load (with Cream of Wheat). Remember, with a rifle barrel, it has a longer in-bore distance to travel so you want to be careful in any load reduction so as not to stick a bullet in the rifle barrel. If you go for a true solution to the real problem, you won't have to do any of that anyway.
Let me know if I haven't interpreted your problem as you intended.