Hm. There are several problems here.
Rupert was born in 1619. So , unless he is to live a Biblical lifespan, an accession to the throne must take place before the turn of the century , or very little after ward.
The suggestion that an early death of Car II, overlooks the fact that , by the rules of descent, both the King's brother James Duke of York; James's two daughters, Mary and Ann, and the descendants of the latter ; William III of Holland; Rupert's own older brother and nephew; and a good number of descendants of Charles's sister (since Romish claimants are not yet proscribed) have precedence of him. It would seem unlikely that all could be fortuitously eliminated.
If Rupert could somehow live to 1714 , it is possible that he might be declared as successor in preference to Sophie, most of the other claimants having in the mean time been removed, either by death or proscription. (The actual declaration would be in 1701 when he was "only" 82). But he would have to live to be 95! Remarkable, though not impossible.
By the laws of descent, Rupert, if living and Protestant in 1701 would have a better claim than Sophie (who was his younger sister). Whether that claim would be sufficient, in the absence of his having an heir, is questionable. But by no means impossible.
So, the best option would be for Rupert , firstly to marry a Protestant and produce an heir , and secondly live for a /very/ long time.