Shower Drain Horizontal Before Trap?

I'm thinking of adding an upstairs bath above a rather ornate living room ceiling that I'd rather not cut into. Is it OK to raise the level of the upstairs fiberglass shower pan (maybe 6 inches) and then have the drain line from the shower pan run horizontally at a minimum slope for maybe 3 feet before adding a trap? The idea is to not cut into the existing upstairs floor deck until the shower drain line runs over an area of attic that I don't mind cutting into. I'd have access to check the trap there via a clean-out cap instead of right at the shower drain.

Raised showers or toilets invite some really nasty comments from Mike Holmes about "do it right"

The longer the pipe between the drain opening and the trap means the more of the pipe that can accumulate stuff like sludge, hair, dead skin, soap scum, etc. The trap is what isolates the room from the rest of the sewer. After awhile, you probably won't like a long trap arm!

You might consider a trench drain that you could install over one end that is where you could install the trap. A little more involved, but in some ways, easier since you only need one slope rather than a 'funnel', it's a single sloped plane.