Pandas: Charting 3 months of quotes with a benchmark

I have a df with the daily "Adj Close" (from Yahoo) for many stocks that I want to chart compared to the SPY.

            AAPL     ABC  ...    SPY
Date 
2016-03-10  100.56  85.79      198.52
2016-03-11  101.64  89.14      201.72
...         
2016-06-09  99.65   76.17      212.08
2016-06-10  98.83   76.46      210.07

I want to chart the last 3 months for each stock except SPY (the benchmark). Each chart should compare the evolution of the stock to the evolution of the SPY.

This means that, for example, for charting AAPL, the benchmark SPY_AAPL should be calculated as:

SPY_AAPL = df['SPY'] / 198.52 * 100.56

...so that the first point of AAPL hovers over that of "SPY_AAPL". Charting the other stocks requires similar calculations...

SPY_ABC = df['SPY'] / 198.52 * 85.79

I am not sure the auxiliary columns (SPY_AAPL, SPT_ABC...) must be added to the df. Perpaps they can be calculated "on the fly".

The "family of charts" could perhaps be in a "for loop"

for x in df.columns:    # how to remove the SPY here?
    df[x].tail(66).plot()    # 66 is approx 3 months
    # SPY_XXX.tail(66).plot()   # here the benchmark
    plt.show()

Any help is highly appreciated.