In Sau Sakhi there were three types of Sikhs.
Sahijdhari ie without 5Ks
Khande Da Pahili(one baptised by sabre as done knowdays).
Charan Pahili(that Sikh perhpas which got baptised before Baptism of sabre was statred).it may be there that it could have continuded after Khande Bate Da amrit till it was not totaly over taken.
the Vidhi or way of making such baptism is temred as ,Soak water with corner of Gurugranth Sahib Ji's covering cloath and drink that water.
Das read it from Pratap singh Mehita version of Sau Sakhi and he in brakect rights that this should happen where living Guru(Tenth master perhaps) is absent but in origeonal text this is not writtan so it could be just an attempt to jutisfy living Guru.But Das is awwre that Namdhair brethern also undergo baptim of Sabre at present.
but if Charan Pahil needs to be revived then onto Guru Granth sahib Ji,it may not be a Bad idea,rest Panth has to decide.