[boost] xpressive and white space skipping

Hi We are using xpressive with a grammar to match certain patterns. In some cases, we have the need to ignore white spaces. Using dynamic regexes, this can be achieved with the ignore_white_space constant. Is there a way to ignore white spaces using a grammar in xpressive other than modifying the grammar itself? We know spirit is an option, but we need to evaluate parsing speed with as many methods as possible. Thanks in advance. Cheers Jorge