If you're not limiting yourself to an arcpy solution, what you're describing sounds like fairly common practice with ArcObjects - there is a 'Buffer Snap Agent' sample here:
Buffer snap agent
http://resources.arcgis.com/en/help/arcobjects-net/conceptualhelp/index.html#/d/000100000334000000.htm
I haven't tested it but was interested in the VB.NET logic - that logic setting your min/max search distance (your outer buffer) and snap to distance (your inner buffer) is in the function, snippet copied from the published sample below. In this sample the distances are hard-coded, as you can see...
(http://resources.arcgis.com/en/help/arcobjects-net/conceptualhelp/index.html#//000100000886000000)
Public Function Snap(ByVal geom As IGeometry, ByVal point As IPoint, ByVal tolerance As Double) As Boolean Implements IEngineSnapAgent.Snap
GetFeatureClass()
Dim b_setNewFeatureCache As Boolean = False
If m_featureClass Is Nothing Or m_editor Is Nothing Then
Return False
End If
If m_featureClass.ShapeType <> esriGeometryType.esriGeometryPoint Then
Return False
End If
'Check if a feature cache has been created.
If Not b_setNewFeatureCache Then
m_featureCache = New FeatureCache()
b_setNewFeatureCache = True
End If
'Fill the New Cache with the geometries.
'It is up to the developer to choose an appropriate value
'given the map units and the scale at which editing will be undertaken.
FillCache(m_featureClass, point, 10000)
Dim proximityOp As IProximityOperator = DirectCast(point, IProximityOperator)
Dim minDist As Double = tolerance
Dim cachePt As IPoint = New PointClass()
Dim snapPt As IPoint = New PointClass()
Dim outPoly As IPolygon = New PolygonClass()
Dim topoOp As ITopologicalOperator
Dim feature As IFeature
Dim Index As Integer = 0
Dim Count As Integer
For Count = 0 To m_featureCache.Count - 1 Step Count + 1
feature = m_featureCache.Feature(Count)
cachePt = feature.Shape
topoOp = cachePt
'Set the buffer distance to an appropriate value
'given the map units and data being edited
outPoly = topoOp.Buffer(1000)
Dim Dist As Double = proximityOp.ReturnDistance(outPoly)
If Dist < minDist Then
Index = Count
minDist = Dist
End If
Next
'Make sure minDist is within the search tolerance.
If minDist >= tolerance Then
Return False
End If
'Retrieve the feature and its part again.
feature = m_featureCache.Feature(Index)
cachePt = feature.Shape
topoOp = cachePt
'Set the buffer distance to an appropriate value
'given the map units and data being edited
outPoly = topoOp.Buffer(1000)
proximityOp = outPoly
snapPt = proximityOp.ReturnNearestPoint(point, esriSegmentExtension.esriNoExtension)
'Since point was passed in ByValue, we have to modify its values instead.
'of giving it a new address.
point.PutCoords(snapPt.X, snapPt.Y)
Return True
End Function
