You can try to do this by adding a second x-axis. Please find below a code you'll need to adapt to your problem. I guess there are better ways to do that but it should works.
from matplotlib.ticker import MultipleLocator
import numpy as np
import matplotlib.pyplot as plt
import seaborn as sns
x = np.arange(1000)
x2 = np.arange(1000)*2
y = np.sin(x/100.)
fig = plt.figure()
ax = plt.subplot(111)
sns.lineplot(x, y)
plt.xlim(0, 1000)
ax.xaxis.set_major_locator(MultipleLocator(200))
ax2 = ax.twiny()
sns.lineplot(x2, y, visible=False)
plt.xlim(0, 2000)
ax2.xaxis.set_major_locator(MultipleLocator(400))
ax2.spines['top'].set_position(('axes', -0.15))
ax2.spines['top'].set_visible(False)
plt.tick_params(which='both', top=False)
