Need way to cover V-joint panelling join on underside of stair

Hi can the forum please help me ... I have used MDF "colonial" V-jointed MDF panelling to line the space under a stairway to create a little computer room. Have used Porta stained oak profile strips to cover the wall corner joints (tri-quad) and the ceiling cornice lines.

The trouble now is the joints on the soffit (underside) of the stairs, which meets at an angle of 150 deg approx (one inner and one outer join, across the stair tread). It seems no combination of pre-manufactured profiles will cover the gap. I had thought I could route something, but now realise I need a table saw (probably) which I don't have, and can't imagine using a circular saw accurately enough to cut 900 mm cover strips to maybe 20 mm width at a bevel angle ...

The photo shows the underside of the stair going away to the right, and the joint to be covered.

Does anyone know of a way to neatly cover this line, and a similar one where the stair soffit panelling meets the wall to the right ... with a timber cover strip (I don't want to just bog the joint up, because it will look bodgy with the V-lined panelling ...).

Any suggestions welcomed.

Given any thought to running some cornice?

You could buy some small dar clear pine and mark an edge for a 75º bevel and plane to the line, then cut it into 2 pieces of correct length and glue it edge to edge to give the 150º moulding you need.

Sounds easy on pixels:)

Cheers
Michael

two pieces of doorstop, 32x12 and angle the edge as required.

A bit of scotia, quad or fillet moulding for the 90 deg joins and ThePope's idea for the 150 deg one. If the gap is consistent, you might get a bit of quad to sit in there.

Thanks everyone for the suggestions. I had been thinking along the lines of mic-d and ThePope but wanted to check that there wasn't an old chippie trick first ... seems I'll have to hand plane to 75 degrees and then cut in halves as suggested.

Thanks again for the suggestions ... great forum.