As the title says. How can we have the Tsarists be a significant force in the RCW?
Have a better candidate for Tsar available?
I am no expert on the time but I get the impression that the candidates for Tsar were not very impressive. Have one with good public opinion and some success both administratively and militarily and you probably would have a significant number of people flocking to him or her
For a better candidate, your best bet would be to have Grand Duke Michael, Emperor Nicholas II's brother and second in line after Tsesarevich Alexei, not be arrested by the provisional government, and later executed by the bolsheviks. He was reportedly fairly liberal (or as liberal as one could expect from a Romanov) so to me he seems to be your best bet.
One question though: who would succeed Grand Duke Mikhail since he did not marry anyone?