Excerpts taken from Naruto Manga Chapter 501-503
Lets look at the following images from the manga,
From image 1> We see Madara* (Who was later shown to be Obito) extracting the kyubi from Kushina's body.
2> This is where he summons the kyubi into the village
3> In the conversation between Madara and Minato, Madara says,
A contract seal...
4> Finishes off the fight between the two.
Now, based on these images we can deduce that it is not always a scroll that is needed to create a summoning contract. A scroll may be one of the ways in which such a contract be created. The sign that is done in the scroll is a "seal" that seals the contract.
So, considering what Madara said about Minato trying to place a contract seal we can deduce that there are other ways to seal a contract. Now when did Madara do it? That must have been done after Madara had the kyubi under genjutsu and before Minato came back for the final showdown between the two.
Now coming back to your question, there are two stages to controlling a beast or summoning animal. The first is where you put the target under genjutsu and manipulate them, the other is to put them under a contract. It seems that Madara has first put the kyubi under genjutsu and then he sealed a contract with the kyubi using some sort of contract seal.
*I am referring to Obito as Madara here because at that point of the manga the character was known to be Madara himself. Which was changed as the plot progressed.