As a CFI multi I think clarification is needed. No multi rating is required for solo. A multi CFI should be able to sign off a student solo endorsement. The two seats are available for dual training. The experimental exemption mentioned earlier should allow solo flight provided the operating limitations do not require the multi rating. However, if the operating limitations do require the rating, a solo sign off to gain proficiency should be possible. I say "should" because the FARs have some language that is unclear about solo sign off of a student when the "student" is a rated pilot. This has muddied the waters for some power pilots getting a glider rating. i am willing to help as much as possible in the certification area.