No. But you can add the routes to your schedule, get the staff for them, do everything in advance, and then when slots appear, all you need to do is open the route, hit edit, hit confirm, and you're done. Much less hassle.
There's also a benefit if you're not in an airport that's slot restricted. Say you've got 50+ planes on order for this game year, you'll be busy at work during the week, but have a free weekend. So spend a few hours creating all your routes for all your planes, without buying slots, and when they turn up, all you have to do is edit the route, buy the slots, assign it to a plane. Instead of having to go through all the route planning & creation. Much quicker & easier, allows you to do the time intensive stuff when it's most convenient, instead of having to do it as planes arrive.