Lantus build up?

Hi all! Had a chat with my diabetes educator this morning about me going high as a kite in my racing (tris). She mentioned that i could take an extra 4 units of lantus (injected) about 2-3 hrs before the race. I was always under the assumption that if you wanted more (or less) basal in the system, it 'builds up' over time? So if i wanted to try and bring racing highs down from more lantus i would have to start injecting extra lantus several days before the actual race? My educator stated that it wasnt true and lantus doesnt build up so to speak and a one off extra injection should help on the day. Anyone have any input on this?