比⋯⋯更 / 还
bǐ …… gèng / hái
Expressing "even more" with "geng" or "hai"
更 and 还 are the only intensifiers a 比 sentence allows, and they go before the adjective.
Noun 1 + 比 + Noun 2 + 更 / 还 + Adj.
How it works
他比姚明还高 — he's even taller than Yao Ming. The 还 says the second person is remarkable, given that the first already is.
更 and 还 are near-identical here; 还 sounds slightly more surprised.
This is the answer to "how do I say 'much taller'?" without breaking the no-很 rule.
Examples
tā bǐ yáo míng hái gāo
他比姚明还高。
He's even taller than Yao Ming.
jīn tiān bǐ zuó tiān gèng lěng
今天比昨天更冷。
Today is even colder than yesterday.
zhè ge bǐ nà ge hái guì
这个比那个还贵。
This one is even more expensive than that one.