Objectives We used a method rarely seen in cancer behavioral trials to explore methods of overcoming difficulties often seen in randomized controlled trials. We report our experiences of the adapted Zelen design, so that other researchers can consider this approach for behavioral trials. Study Design and Setting The adapted Zelen design was used to explore the effects of exercise on multiple myeloma patients fatigue, quality of life, and physical outcomes. All participants consented to an observational cohort study of lifestyle factors but were unaware of subsequent randomization to remain in cohort only group or be offered an exercise intervention requiring second consent. Results There was lower than expected uptake to the exercise offered group (57%), so the length of recruitment increased from 24 to 29 months to ensure power was reached. At enrollment, patients were unaware of the potential increased commitment, and as a result, 62% of participants allocated to the intervention declined because of the extra time/travel commitment required. This emulates clinical settings and suggests improvements in intervention delivery are required. Our findings suggest that the adapted Zelen design may be useful in limiting dropout of controls due to dissatisfaction from group allocation, or contamination of control arm. Conclusion Future use of this design warrants careful consideration of the study resources and recruitment time frames required but holds potential value in reducing contamination, control group dissatisfaction, and resulting dropout. Adapted Zelen design reduces selection bias and therefore gives clinicians a better understanding of acceptability in clinical settings. Future studies should evaluate control group experiences of the design and formally record contamination throughout the study to confirm its acceptability.