Hair root color problem

I usually get highlights and a toner nothing else done but recently I just dont have the time to go to a hairstylist but my roots are growing out about 2 inches about now. I want to know what is a temp solution that I may do myself till I get a chance to go to professional, my schedule will be crazy for about a month. My highlights are a honey blonde and my roots are a light to med. brown. I was thinking of doing like a non permanent hair wash or toner will that help my roots. Maybe add something to my hightlights to make then appear a little darker but the problem with that is Im not sure if I will be able to highlight my hair again and I do not want to damamge my hair because it is straight and long. So please help, thank you.
Isella