Here's an off the wall idea that may spark some inspiration.
Take a clear plexiglass/plastic tube the size of the nozzles. Attach them to the nozzles and use them as the stand. Here's the catch - Harriers don't have smoke exhaust persay but they do kick up a bunch of dust. And the heat makes the air 'shimmer' like a mirage.
So - paint (AB) the tubes in a buff or dull coat texture so they distort the light going through them. The size will mimic the nozzle thrust.

It's a thought - hope it helps.

Either that or small thin plastic rods connecting to each wheel.

That sounds like a great idea, and I see the dilema. I have seen one Harrier built the way you are asking at a local hobby shop on display.
What he did was used rods going up to the jet nozzles and covered them with cotton and painted them like it was exhaust.
The problem with that is Harriers don't smoke when the hover the exhaust is clear. It looked ok but the smoke threw the effect off a little.
What you could try is running an L shaped bracket or rod down the centerline of the Bird letting the gunpod and ordnance hide it and stick the long end in the base. then surround the long piece with whatever trees,saddunes or whatever terrain there would be around it.
Harriers usually don't use strict verticle takoffs unless they are on auxillary landing fields or at Foward refueling points.
Plus using the rod will give the option of angling the the nose of the Harrier to give the aceeleration of assent. From 0 degrees of a straight hover to about 45 degrees a full power "POP" as we used to call it.
Hope this gives you and idea and hope you come up with something. Cause I would love to see this when it was done
Paul

Either that or small thin plastic rods connecting to each wheel.

Here's an off the wall idea that may spark some inspiration.
Take a clear plexiglass/plastic tube the size of the nozzles. Attach them to the nozzles and use them as the stand. Here's the catch - Harriers don't have smoke exhaust persay but they do kick up a bunch of dust. And the heat makes the air 'shimmer' like a mirage.
So - paint (AB) the tubes in a buff or dull coat texture so they distort the light going through them. The size will mimic the nozzle thrust.

It's a thought - hope it helps.

Either that or small thin plastic rods connecting to each wheel.

At the IPMS Stockholm Open held a few weeks ago there was a model suspended in air by magnets!! The guy had to tie down so it wasn't thrown off the magnetic field. This might be hard to do with what you are doing in 1/48, because of the weight...

Thought it was a neat idea!!