Among the documents in the archive of the Livonian Governor General there is a fragment of Lewenhaupt's letter book for the autumn of 1707. Among the copies of letters is a fairly long one to the King, which (as far I know) isn't preserved elsewhere. It's dated Mitau 13 September 1707 and starts by describing the military situation in Courland and Lithuania. Prince Wisniowiecki is positioned near Birsen and the enemy has advanced as if the intention was to the Prince's forces. Lewenhaupt had sent some cavalry in support, which the enemy (according to Lewenhaupt) believed were the first units from the approaching Royal army (which of course was far away in Poland). The enemy had as a result of this hastily retreated. Bauer was advancing from Kaunas with orders to fall back if the King's army approached. Repnin and a considerable force of infantry remained at Vilnius. His plan was to attack Courland if the Swedish main army stopped in Silesia. Lewenhaupt intended to stay close to Riga until the main army approached. The supply problems were considerable, so if he could not get assistance from Stockholm the King himself would have to intervene. Lewenhaupt also informed Charles that the was working on clearing up the remaining differences between Wisniowiecki and Sapieha. Both had visited Lewenhaupt both on the 11th and the 12th. Good progress had been made, but the most difficult item remained - the transfer of Wisniiwcki's forces to the Hetman. Wisniowiecki claimed (and Lewenhaupt agreed) that most of his units would desert if this was forced upon them. Lewenhaupt emphasized that he had always found Wisniowiecki to be an honest and truthful supporter of King Stanislaw.
This letter preceeds the discussion Lewenhaupt in his memoirs claims he had with the King during his visit to the latters headquarters in the spring of 1708, during which Charles supposedly got upset when Lewenhaupt suggested that Wisniowiecki had shown himself to be much more reliable and useful than Hetman Sapieha ever had been (a pretty bold statement as Lewenhaupt well knew the King's strong and long support for the Sapieha family).
Source: LVVA, fond 7349, op. 1, vol. 331