Ndef, filter, filterIn

Is there a good reason why Ndef has an instance method for filter but not for filterIn? Basically, I’d like to be able to write this:

Ndef(\a).filterIn(1, {|i| PitchShift.ar(i, pitchRatio: LFTri.kr(1/10).range(0.5,1.5))})

Instead of this:

Ndef(\a)[1] = \filterIn -> {|i| PitchShift.ar(i, pitchRatio: LFTri.kr(1/10).range(0.5,1.5))}

Is it easy to add that method?

Answering own question:

+ Ndef {	filterIn { | i, func |
		this.put(i, \filterIn -> func)