Yes, it is permissible for him to make up the days separately, because Allaah says (interpretation of the meaning):
âand whoever is ill or on a journey, the same number of days which one did not observe Sawm (fasts) must be made up from other daysâ
He did not stipulate that the days be made up consecutively.
And Allaah is the source of strength, May Allaah send blessings and peace upon our Prophet Muhammad and his family and companions. End quote.
Standing Committee for Academic Research and Issuing Fatwas
Fataawa al-Lajnah al-Daaâimah liâl-Buhooth al-âIlmiyyah waâl-Ifta (10/346).