What you would want to do is have the floor be able to receive decals and your character not receive Decals (so that the shadow draws only on the floor). Then have the decal be always under the character. This way, the decal (e.g. a blob) will behave like a fake shadow.
Something to notice though is that a decal has a finite range so if your character jumps you might want to either ignore the Character’s Z value (and have the decal always at a fixed Z value, but this might be an issue when working with different heights) or have the decal’s height big enough so that the shadow is always projected even when the character jumps.
I just did a quick test and it was very easy to add a blob shadow, but thanks to adding decal into my google searches, I’ve now found a few other tutorials on the subject.