I've been thinking about how you could use a five-suited Stardeck to play five-handed euchre. Here are my thoughts, in disorganized form; maybe someone can take them (or point me to rules that already exist).
1) The rank of cards in a suit would be: Jack of suit, Jack of off-suit, then Jack of Stars; then Ace, King, Queen, 10, 9. Trump cards outrank non-trump. Star cards are always trump, BUT they rank below regular trump (except for the Jack of Stars, as noted). Alternative: star cards are just another suit, but never trump unless Stars are trump.
2) Player to left of dealer has first chance to bid. Then the right to join the bidder as partner is offered to each player to bidder's left. The first player to agree becomes bidder's partner for that hand. Bidder can choose to go alone for bonus points. If no one bids to join, and bidder hasn't chosen to go alone, then dealer must join. In any case, the second bidder gets the face-up card.
3) Each player keeps his own score. There aren't permanent partnerships as there are in 4-handed euchre. A win is worth two points to each of the bidder and joiner. Otherwise, each non-bidder gets one point. A loner is worth 4 points, or 2 to each non-bidder.
4) There are six cards in each of the five suits. Deal five cards to each player and turn up one card. That means there are four cards hidden. If the card is a non-star suit, then that suit is trump (as normal euchre) if a bidder bids. If the card is a star, then stars are trump (rank of cards is Jack of Stars, Jack of Clubs, Jack of Diamonds, Jack of Hearts, Jack of Spades (the four suits in alphabetical order), Ace of Stars, King, Queen, 10, 9. Yes, there are more trump cards when Stars are trump. Alternative rule: Jack of Stars is top trump, then all Jacks (but first Jack played wins the trick), then Ace, King, Queen, 10, 9.
That's all I have so far; I haven't playtested this but am hoping to find some players who will give this a try.