Yeah, a full over-the-shoulder latex prosthetic with build in/under support is what you'd need to make that totally seamless.
I agree with Penlowe that a harness under a nude leotard is the best low-budget idea.
Though I'm not sure why you couldn't use the dress for support like with the bow just because you are also attaching the bow to it ? What precludes you from doing both ? Is the dress not build structurally sound enough ?
Disclaimer : This post written by a Grumpy Old Man
Actually in the pipes:
- Remaking Ser Loras doublet.
- Luke Skywalker, A New Hope
- Wind Waker starter costume in swim material
Eventually: Paul from Dune, Faramir, Harry Sullivan