Decisions taken in 1943 sent the B-29s to the Pacific first. Had the war in Europe gone on longer there were plans for 9 B-29 groups in the UK. No B-29 units existed in the ETO during WWII.
According to Roger Freeman in 'The Mighty Eighth', a single B-29 was diverted from delivery to the CBI theater in March 1944 for technical evaluation by the 8th AF and to deceive the Germans regarding B-29 deployment plans to the UK. It visited Glatton and Knettishall.