URGENT: Prompt Macro as Text Default of another Prompt Macro

[Tore2015]

I am in a bind, and need assistance if possible!!

Need to use another prompt macro as the value for the default text within another macro.  Here is the background:  I am trying to set the range for the x-axis of a chart to show a set number of months by default, and then the min and max months will be changed dynamically by prompts.  So the data item I am using for the range is as follows:

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intersect(lastPeriods(-9999, (#prompt('p_Month1','memberuniquename','item(tail([People Pack EOP].[Time Dim].[Time].[Month]),0)')#)),
lastPeriods(9999,(#prompt('p_Month2','memberuniquename','item(tail([People Pack EOP].[Time Dim].[Time].[Month]),0)')#)))

The first part of this expression works as expected, but the 2nd prompt 'p_Month2', will need to have a default of 12 months back from the tail of the Month level.  Below is a separate expression that can get this member 12 months from the tail:

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head(lastPeriods(12,item(#prompt('p_Month','memberuniquename','tail(members([People Pack EOP].[Time Dim].[Time].[Month]))')#,0)))

So my dilemma, is how to combine these expressions into one expression which will be used for the range,,which will be dynamic?????

First...does this make sense and Second...is there a solution?