Problems with custom buff skill

I have problems with a custom skill based on the Scroll of Speed. I made it a hero skill with levels and a different duration on each level. Furthermore I want it to give a damage bonus to nearby units, but I can't get this to work.
I tried it by creating a second custom skill based on roar and making a trigger that recognizes if the speed skill is cast; then it would give the hero the damage skill, issue an order to the hero to cast the damage skill and remove the damage skill. However, I cannot issue an order to cast a custom skill.

Is there is a way to do it as I intended? And if not, is there another way to get this effect?

You have to work with custom text to force a unit to work with a custom skill.

I won't go into it here. Either scanning the FAQ or using the Search feature will yield what you want, I guarentee it.