The sad answer is - you can't achieve what you are looking for.
You could use "substitute Omega=10^3 mOmega", but this will destroy what "explicit" does.
"explicit" never worked the way people looking for creating a step by step documentation wanted it to work and it got even worse in Prime.
In Prime we can't even hide the ugly keywords of the symbolics as we can in real Mathcad (=Mathcad 15 and below) and we can't make that arrow look like a simple equal sign.
Also the problem of expressions being too long for a page width never was addressed satisfactory. I have seen people making screenshots of such way too long expressions, inserting the pictures them in the sheet and shrink them to fit the page width. Horrible!!