The verb 'to wee' is - I presume - intransitive. So perhaps, 'to wee into his pants'? or has 'to wee his pants' acquired sufficient usage that it is an accepted form?
The present tense : I wee. The perfect tense here - is it actually 'he has weed'? - might it not be: 'he has *wee-ed' = 'wee'd', or *'weeed'?
Or is it like 'see / saw / seen' - 'he has ween'??