Ryusuta
Smash Master
As Nikes mentioned, yes, you can easily up B before double jumping. A lot of Yoshi players prefer to disable tap jump for this very reason.
I play with tap jump on, but that actually doesn't stop you from being able to do it. There's a few different ways with tap jump to do it. The most immediate way is to do a "tilt" up B. Yes, actually tilt the stick upwards as if you were doing an up tilt in the air and press B. With practice, this becomes very easy. You can also buffer into pressing up during lag or hitstun and it won't use your second jump.
I play with tap jump on, but that actually doesn't stop you from being able to do it. There's a few different ways with tap jump to do it. The most immediate way is to do a "tilt" up B. Yes, actually tilt the stick upwards as if you were doing an up tilt in the air and press B. With practice, this becomes very easy. You can also buffer into pressing up during lag or hitstun and it won't use your second jump.