In one of the many LVVA fond 7349 volumes which contain documents once belonging to Carl Schirren there are a couple of odd Patkul items which suggest that the future conspirator at some point was entrusted with a diplomatic mission to the Duke of Courland (LVVA, fond 7349, op. 2, vol. 200). Unfortunately neither of the two drafts are dated, but Schirren's assumption (in a covering note) was that they are older than 1690. Patkul's task concerned a problem which for a long time irritated both the merchants in Riga and the Swedish government, i.e. the many small "illegal" harbors along the coast of Courland (for this issue, see for example Arnold Soom's Der baltische Getreidehandel im 17 Jahrhunderts, pp. 163 ff.).
Is it possible to date the two items (a letter to the Duke and the instruction for Patkul? Well, they are obviously younger than May 1687 as he called "Captain". If the documents were issued by Governor General Hastfer it would seem likely that it was done during the periods he was present in Riga (July 1687-May 1689, June-October 1690, June-October 1693 or August-December 1695). Based on Patkul's later activities as a spokesman of the Livonian nobility only the first two periods are reasonable possibilities and the first one the more likely. When scanning Hastfer's outgoing letters I soon found an interesting item, dated 22 October 1688 (LVVA, fond 7349, op. 1, vol. 40, pp. 639-641). In a letter to Charles XI Hastfer reports that he has appointed a commission consisting of Leonhard Gustaf von Budberg, H. G. Trautvetter and Captain Patkul. There task was to look into a border conflict between the Livonian estate Pulkarn and Baldohn in Courland. The interesting thing about the composition of this commission is that Budberg was a "Landrat", Trautvetter a member of the court of appeal in Dorpat and Patkul a simple captain. So why this choice? Well, this as well as Patkul's appointment as captain in 1687 (and Patkul's subsequent letter of gratitude to Hastfer) suggests that he during this period of time was quite close to the Governor General, indeed something of a protegé. Whether this commission and Patkul's mission of discussing trade issues were connected I don't know, but if not it would seem likely that the commission came first.
In his work about the struggle of the Livonian nobility against Swedish absolutism Alvin Isberg suggests that Patkul made himself a name as a outspoken defender of old privileges in private meeting with other nobles in 1689. My hunch is that was quite different - Patkul was perceived as being close to Hastfer and because of this (and his own ability) quickly became a rising star. Once he reached the top Patkul turned out to have a very different agenda...