Within the first period of the CORBEL project, the goal of work package 4 (WP4) is to drive the development of shared services between European biological and medical science research infrastructures (BMS RIs) and to establish their maturity towards open user access. To accomplish this, we will employ use cases that follow defined pipelines covering a broad range of scientific research fields and involving expertise and techniques distributed across distinct RIs in several European countries. The RIs involved in CORBEL are currently at different operational stages with respect to their legal and functional development. This is reflected in their accessibility for external users. Whereas some RIs have already procedures in place that allow external scientists to get access to their core facilities, other RIs are still in the process of defining access procedures and establishing their service offers. Therefore, in CORBEL for the first time, eleven BMS RIs on the ESFRI roadmap (European Strategic Forum on Research Infrastructures) want to enable user access for projects that require combined advanced services across different infrastructures. This requires the definition of an appropriate strategy, which has been developed during the first month of the project. This document presents the strategy for supporting user access within pilot use cases. After several meetings, WP4 partners agreed to apply a two-step process to identify well-suited pilot users and projects. Since most joint service pipelines need to be developed, tested and refined, BMS RIs partners have started to engage with a first generation of pilot users based on their pre-existing contacts. In a second step, an open call will be prepared and publicly advertised. This will provide not only high visibility for CORBEL and all involved BMS RIs, but also critical credibility to make the common services broadly established and openly accessible beyond the project duration.