It's possible to create one way pricing, city pairs, for each of your aircraft. One way pricing will overrule the pricing profile when the trip is the exact match to one way itinerary. For multi leg and rounds trips one way pricing will not applied.

When you set up a one way pricing between two airports, you can choose when this price should apply with Days Out setting. If you put 0 in this settings, one way pricing will always apply for this route, regardless to your schedule availability. If you put 10 days out, one way pricing will apply for requests in 10 days and will not look at aircraft availability.

How to set it up:
When logged into Avinode, go to the Aircraft tab, chose Fleet.

For the aircraft you want to add the one-way price to, click on edit to the right on the page, the little pencil symbol.
Chose the tab called One way pricing. 

To the right on the next page, click on "Create new".
Select the route, Days out and Fixed price for the route:

Click save and the fixed rate is applied for this aircraft.